[clang] [Serialization] Downgrade inconsistent flags from erros to warnings (PR #115416)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `clang` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/8111

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: PCH/pch-dir.c' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: rm -rf /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch
+ rm -rf /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch
RUN: at line 2: mkdir -p /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch
+ mkdir -p /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch
RUN: at line 4: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c-header /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.h -DFOO=foo -o /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch/c.gch
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c-header /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.h -DFOO=foo -o /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch/c.gch
RUN: at line 5: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c-header /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.h -DFOO=bar -o /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch/cbar.gch
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c-header /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.h -DFOO=bar -o /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch/cbar.gch
RUN: at line 6: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c++-header -std=c++98 /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.h -o /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch/cpp.gch
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c++-header -std=c++98 /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.h -o /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h.gch/cpp.gch
RUN: at line 7: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -DFOO=foo -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c -Xclang -print-stats 2> /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.clog
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -DFOO=foo -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c -Xclang -print-stats
RUN: at line 8: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck -check-prefix=CHECK-C /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c < /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.clog
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck -check-prefix=CHECK-C /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c
RUN: at line 9: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -DFOO=bar -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c -Xclang -ast-print > /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.cbarlog
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -DFOO=bar -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c -Xclang -ast-print
RUN: at line 10: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck -check-prefix=CHECK-CBAR /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c < /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.cbarlog
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck -check-prefix=CHECK-CBAR /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c
RUN: at line 11: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c++ -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -std=c++98 -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c -Xclang -print-stats 2> /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.cpplog
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c++ -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -std=c++98 -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c -Xclang -print-stats
RUN: at line 12: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck -check-prefix=CHECK-CPP /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c < /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.cpplog
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck -check-prefix=CHECK-CPP /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c
RUN: at line 14: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c++ -std=c++11 -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c 2> /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.cpp11log
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -x c++ -std=c++11 -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c
RUN: at line 15: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c --check-prefix=CHECK-OPT-DIFF < /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.cpp11log
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c --check-prefix=CHECK-OPT-DIFF
RUN: at line 17: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c 2> /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.missinglog2
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/clang -include /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/test/PCH/Output/pch-dir.c.tmp.h -fsyntax-only /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/clang/test/PCH/pch-dir.c

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/115416