[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 `clang-solaris11-sparcv9` running on `solaris11-sparcv9` while building `clang` at step 4 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/13/builds/1680

Here is the relevant piece of the build log for the reference:
```
Step 4 (build stage 1) failure: 'ninja -j8' (failure)
...
[35/149] Linking CXX executable bin/llvm-ctxprof-util
[36/149] Linking CXX executable bin/llvm-symbolizer
[37/149] Building CXX object tools/clang/lib/FrontendTool/CMakeFiles/obj.clangFrontendTool.dir/ExecuteCompilerInvocation.cpp.o
[38/149] Generating ../../bin/llvm-otool
[39/149] Generating ../../bin/llvm-windres
[40/149] Generating ../../bin/llvm-readelf
[41/149] Generating ../../bin/llvm-addr2line
[42/149] Linking CXX executable bin/llvm-profdata
[43/149] Linking CXX executable bin/yaml2obj
[44/149] Building CXX object tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o
FAILED: tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.cpp.o 
/opt/llvm/17/bin/clang++ -DGTEST_HAS_RTTI=0 -D_CINDEX_LIB_ -D_DEBUG -D_FILE_OFFSET_BITS=64 -D_GLIBCXX_ASSERTIONS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/tools/clang/tools/libclang -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/tools/clang/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include/llvm/Support/Solaris -fPIC -fno-semantic-interposition -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  -O -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 /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp:25:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:164:38: error: member access into incomplete type 'SourceManager'
  164 |     return Context.getSourceManager().isInSystemHeader(D->getLocation());
      |                                      ^
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp:25:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:293:33: error: member access into incomplete type 'SourceManager'
  293 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp:25:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:366:33: error: member access into incomplete type 'SourceManager'
  366 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp:25:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:404:33: error: member access into incomplete type 'SourceManager'
  404 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp:25:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:535:33: error: member access into incomplete type 'SourceManager'
  535 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/tools/libclang/CXExtractAPI.cpp:25:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:581:33: error: member access into incomplete type 'SourceManager'

```

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