[clang] [clang][bytecode] Fix a crash when redeclaring extern globals (PR #164204)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-x86_64-windows` running on `minipc-ryzen-win` while building `clang` at step 7 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/166/builds/3158

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

```
Step 7 (test-build-unified-tree-check-flang) failure: test (failure)
Statistics zeroed
2.186 [36/1/1] Generating VCSRevision.h, __FakeVCSRevision.h
5.175 [1/2/2] Linking CXX executable tools\flang\unittests\Optimizer\FlangOptimizerTests.exe
7.784 [1/1/3] Linking CXX executable tools\flang\unittests\Frontend\FlangFrontendTests.exe
FAILED: [code=4294967295] tools/flang/unittests/Frontend/FlangFrontendTests.exe 
C:\Windows\system32\cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E vs_link_exe --msvc-ver=1944 --intdir=tools\flang\unittests\Frontend\CMakeFiles\FlangFrontendTests.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100261~1.0\x64\rc.exe --mt=C:\PROGRA~2\WI3CF2~1\10\bin\100261~1.0\x64\mt.exe --manifests  -- C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\link.exe /nologo @CMakeFiles\FlangFrontendTests.rsp  /out:tools\flang\unittests\Frontend\FlangFrontendTests.exe /implib:tools\flang\unittests\Frontend\FlangFrontendTests.lib /pdb:tools\flang\unittests\Frontend\FlangFrontendTests.pdb /version:0.0 /machine:x64 /STACK:10000000 /INCREMENTAL:NO /subsystem:console && cd ."
LINK: command "C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\link.exe /nologo @CMakeFiles\FlangFrontendTests.rsp /out:tools\flang\unittests\Frontend\FlangFrontendTests.exe /implib:tools\flang\unittests\Frontend\FlangFrontendTests.lib /pdb:tools\flang\unittests\Frontend\FlangFrontendTests.pdb /version:0.0 /machine:x64 /STACK:10000000 /INCREMENTAL:NO /subsystem:console /MANIFEST:EMBED,ID=1" failed (exit code 1190) with the following output:
LLVMObject.lib(COFFObjectFile.cpp.obj) : fatal error LNK1190: invalid fixup found, type 0x28EC
ninja: build stopped: subcommand failed.
Cache directory:    C:\Users\buildbot-worker\AppData\Local\ccache
Config file:        C:\Users\buildbot-worker\AppData\Local\ccache\ccache.conf
System config file: C:\ProgramData\ccache\ccache.conf
Stats updated:      10/20/25 04:05:53
Local storage:
  Cache size (GB):    5.0 / 5.0 (99.90%)
  Files:            22620
  Hits:                 0
  Misses:               0
  Reads:                0
  Writes:               0

```

</details>

https://github.com/llvm/llvm-project/pull/164204