[clang] [clang][ExtractAPI] Stop dropping fields of nested anonymous record types when they aren't attached to variable declaration (PR #104600)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-clang-x86_64-linux-debian` running on `gribozavr4` while building `clang` at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/6/builds/2375

Here is the relevant piece of the build log for the reference:
```
Step 5 (compile-openmp) failure: build (failure)
...
41.435 [24/8/5229] Linking CXX executable bin/bugpoint
41.443 [23/8/5230] Building CXX object tools/bugpoint-passes/CMakeFiles/BugpointPasses.dir/TestPasses.cpp.o
41.473 [22/8/5231] Linking CXX shared module lib/BugpointPasses.so
41.524 [22/7/5232] Linking CXX executable bin/llvm-lto2
41.543 [22/6/5233] Linking CXX executable bin/clang-linker-wrapper
41.567 [22/5/5234] Linking CXX shared library lib/libLTO.so.20.0git
41.569 [21/5/5235] Creating library symlink lib/libLTO.so
42.317 [21/4/5236] Linking CXX executable bin/clang-scan-deps
42.647 [21/3/5237] Linking CXX executable bin/clang-check
43.269 [21/2/5238] Building CXX object tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o
FAILED: tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes /usr/bin/ccache /usr/bin/clang++ -DGTEST_HAS_RTTI=0 -D_CINDEX_LIB_ -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/b/1/openmp-clang-x86_64-linux-debian/llvm.build/tools/clang/tools/libclang -I/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang -I/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include -I/b/1/openmp-clang-x86_64-linux-debian/llvm.build/tools/clang/include -I/b/1/openmp-clang-x86_64-linux-debian/llvm.build/include -I/b/1/openmp-clang-x86_64-linux-debian/llvm.src/llvm/include -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -Wno-nested-anon-types -O3 -DNDEBUG -fPIC  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -MD -MT tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o -MF tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o.d -o tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o -c /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp
In file included from /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp:25:
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:164:38: error: member access into incomplete type 'clang::SourceManager'
    return Context.getSourceManager().isInSystemHeader(D->getLocation());
                                     ^
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
class SourceManager;
      ^
In file included from /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp:25:
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:293:33: error: member access into incomplete type 'clang::SourceManager'
      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
                                ^
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
class SourceManager;
      ^
In file included from /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp:25:
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:366:33: error: member access into incomplete type 'clang::SourceManager'
      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
                                ^
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
class SourceManager;
      ^
In file included from /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp:25:
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:404:33: error: member access into incomplete type 'clang::SourceManager'
      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
                                ^
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
class SourceManager;
      ^
In file included from /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp:25:
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:535:33: error: member access into incomplete type 'clang::SourceManager'
      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
                                ^
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
class SourceManager;
      ^
In file included from /b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/tools/libclang/CXExtractAPI.cpp:25:
/b/1/openmp-clang-x86_64-linux-debian/llvm.src/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:581:33: error: member access into incomplete type 'clang::SourceManager'

```

https://github.com/llvm/llvm-project/pull/104600