[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-debian-cpp20` running on `clang-debian-cpp20` while building `clang` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/108/builds/2631

Here is the relevant piece of the build log for the reference:
```
Step 5 (build-unified-tree) failure: build (failure)
...
128.771 [13/17/5758] Copying llvm-locstats into /vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/./bin
128.794 [13/16/5759] Linking CXX executable bin/llvm-symbolizer
128.810 [12/16/5760] Generating ../../bin/llvm-addr2line
128.897 [12/15/5761] Linking CXX executable bin/llvm-xray
129.168 [12/14/5762] Linking CXX executable bin/sanstats
129.225 [12/13/5763] Linking CXX executable bin/obj2yaml
129.259 [12/12/5764] Linking CXX executable bin/yaml2obj
129.333 [12/11/5765] Linking CXX executable bin/verify-uselistorder
129.675 [12/10/5766] Linking CXX executable bin/clangd
129.713 [12/9/5767] 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 /usr/bin/clang++-17 -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/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/tools/clang/tools/libclang -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/tools/clang/include -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/include -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/include -Wno-deprecated-enum-enum-conversion -Wno-deprecated-declarations -Wno-deprecated-anon-enum-enum-conversion -Wno-ambiguous-reversed-operator -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 -O3 -DNDEBUG -std=c++20 -fPIC  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -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 /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp
In file included from /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp:25:
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:164:38: error: member access into incomplete type 'SourceManager'
  164 |     return Context.getSourceManager().isInSystemHeader(D->getLocation());
      |                                      ^
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp:25:
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:293:33: error: member access into incomplete type 'SourceManager'
  293 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp:25:
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:366:33: error: member access into incomplete type 'SourceManager'
  366 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp:25:
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:404:33: error: member access into incomplete type 'SourceManager'
  404 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp:25:
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:535:33: error: member access into incomplete type 'SourceManager'
  535 |       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
      |                                 ^
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/Basic/SourceLocation.h:34:7: note: forward declaration of 'clang::SourceManager'
   34 | class SourceManager;
      |       ^
In file included from /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/tools/libclang/CXExtractAPI.cpp:25:
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h:581:33: error: member access into incomplete type 'SourceManager'

```

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