[clang] [clang-format] Fix an assertion failure on comment-only config files (PR #163111)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vla-2stage` running on `linaro-g3-04` while building `clang` at step 12 "ninja check 2".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/41/builds/9680

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

```
Step 12 (ninja check 2) failure: stage 2 checked (failure)
******************** TEST 'SanitizerCommon-lsan-aarch64-Linux :: compress_stack_depot.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/./bin/clang  --driver-mode=g++ -gline-tables-only -fsanitize=leak   -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta  -funwind-tables  -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test -ldl /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp -fsanitize-memory-track-origins=1 -o /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp # RUN: at line 1
+ /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/./bin/clang --driver-mode=g++ -gline-tables-only -fsanitize=leak -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -funwind-tables -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test -ldl /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp -fsanitize-memory-track-origins=1 -o /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp
clang: warning: argument unused during compilation: '-fsanitize-memory-track-origins=1' [-Wunused-command-line-argument]
env LSAN_OPTIONS="compress_stack_depot=0:malloc_context_size=128:verbosity=1"  /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp 2>&1 | FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --implicit-check-not="StackDepot released" # RUN: at line 2
+ env LSAN_OPTIONS=compress_stack_depot=0:malloc_context_size=128:verbosity=1 /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp
+ FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp '--implicit-check-not=StackDepot released'
env LSAN_OPTIONS="compress_stack_depot=-1:malloc_context_size=128:verbosity=1"  /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp 2>&1 | FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS # RUN: at line 3
+ env LSAN_OPTIONS=compress_stack_depot=-1:malloc_context_size=128:verbosity=1 /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp
+ FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS
env LSAN_OPTIONS="compress_stack_depot=-2:malloc_context_size=128:verbosity=1"  /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp 2>&1 | FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS # RUN: at line 4
+ env LSAN_OPTIONS=compress_stack_depot=-2:malloc_context_size=128:verbosity=1 /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp
+ FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS
env LSAN_OPTIONS="compress_stack_depot=1:malloc_context_size=128:verbosity=1"  /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp 2>&1 | FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS,THREAD # RUN: at line 5
+ env LSAN_OPTIONS=compress_stack_depot=1:malloc_context_size=128:verbosity=1 /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp
+ FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS,THREAD
env LSAN_OPTIONS="compress_stack_depot=2:malloc_context_size=128:verbosity=1"  /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp 2>&1 | FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS,THREAD # RUN: at line 6
+ FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp --check-prefixes=COMPRESS,THREAD
+ env LSAN_OPTIONS=compress_stack_depot=2:malloc_context_size=128:verbosity=1 /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/stage2/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/lsan-aarch64-Linux/Output/compress_stack_depot.cpp.tmp
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp:53:14: error: COMPRESS: expected string not found in input
// COMPRESS: StackDepot released {{[0-9]+}}
             ^
<stdin>:12:53: note: scanning from here
LeakSanitizer: StackDepot compression thread started
                                                    ^
<stdin>:13:16: note: possible intended match here
LeakSanitizer: StackDepot compression thread stopped
               ^

Input file: <stdin>
Check file: /home/tcwg-buildbot/worker/clang-aarch64-sve-vla-2stage/llvm/compiler-rt/test/sanitizer_common/TestCases/compress_stack_depot.cpp

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            .
            .
            .
            7: ==3783681==Unregistered root region at 0xec59c8603560 of size 224 
            8: ==3783681==Unregistered root region at 0xec59c9400780 of size 32 
            9: ==3783681==Installed the sigaction for signal 11 
           10: ==3783681==Installed the sigaction for signal 7 
           11: ==3783681==Installed the sigaction for signal 8 
           12: LeakSanitizer: StackDepot compression thread started 
check:53'0                                                         X error: no match found
...

```

</details>

https://github.com/llvm/llvm-project/pull/163111