[clang] [Thread Analysis] Fix a bug in context update in alias-analysis (PR #178952)

[Marco Elver via cfe-commits]

melver wrote:

Something is wrong with this change, see CI failure:

```
FAILED: compiler-rt/lib/scudo/standalone/tests/ScudoUnitTestsObjects.primary_test.cpp.x86_64.o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/runtimes/runtimes-bins/compiler-rt/lib/scudo/standalone/tests/ScudoUnitTestsObjects.primary_test.cpp.x86_64.o
cd /home/gha/actions-runner/_work/llvm-project/llvm-project/build/runtimes/runtimes-bins/compiler-rt/lib/scudo/standalone/tests && /home/gha/actions-runner/_work/llvm-project/llvm-project/build/./bin/clang++ -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Werror -Wno-unused-parameter -Wno-unknown-warning-option -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -I/home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/include -g -Wno-covered-switch-default -Wno-suggest-override -DGTEST_NO_LLVM_SUPPORT=1 -DGTEST_HAS_RTTI=0 -I/home/gha/actions-runner/_work/llvm-project/llvm-project/runtimes/../third-party/unittest/googletest/include -I/home/gha/actions-runner/_work/llvm-project/llvm-project/runtimes/../third-party/unittest/googletest -I/home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/include -I/home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib -I/home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/scudo/standalone -I/home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/scudo/standalone/include -DGTEST_HAS_RTTI=0 -g -Wconversion -Wno-mismatched-new-delete -DGWP_ASAN_HOOKS -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -Werror=thread-safety -m64 -c -o ScudoUnitTestsObjects.primary_test.cpp.x86_64.o /home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/scudo/standalone/tests/primary_test.cpp
In file included from /home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/scudo/standalone/tests/primary_test.cpp:11:
In file included from /home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/scudo/standalone/allocator_config.h:16:
/home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/scudo/standalone/primary32.h:306:33: error: reading variable 'FreeListInfo' requires holding mutex 'getSizeClassInfo(I).Mutex' [-Werror,-Wthread-safety-precise]
306 |     for (BatchGroupT &BG : Sci->FreeListInfo.BlockList) {
|                                 ^
```

https://github.com/llvm/llvm-project/pull/178952