[clang] [Clang] Fix dependent local class instantiation bugs (PR #134038)

[Daniel Thornburgh via cfe-commits]

mysterymath wrote:

This looks to be the likely culprit for a clang crash in the Fuchsia build:

```
[21173/168418](63) CXX host_x64/obj/src/developer/debug/zxdb/client/libclient.map_setting_store.cc.o
FAILED: [code=1] host_x64/obj/src/developer/debug/zxdb/client/libclient.map_setting_store.cc.o
../../prebuilt/third_party/clang/custom/bin/clang++ -MD -MF host_x64/obj/src/developer/debug/zxdb/client/libclient.map_setting_store.cc.o.d -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -DCURL_NO_OLDIES -DLLVM_USING_OLD_PREBUILT -DRAPIDJSON_HAS_STDSTRING -DRAPIDJSON_HAS_CXX11_RANGE_FOR -DRAPIDJSON_HAS_CXX11_RVALUE_REFS -DRAPIDJSON_HAS_CXX11_TYPETRAITS -DRAPIDJSON...
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: ../../prebuilt/third_party/clang/custom/bin/clang++ -MD -MF host_x64/obj/src/developer/debug/zxdb/client/libclient.map_setting_store.cc.o.d -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -DCURL_NO_OLDIES -DLLVM_USING_OLD_PREBUILT -DRAPIDJSON_HAS_STDSTRING -DRAPIDJSON_HAS_CXX11_RANGE_FOR -DRAPIDJSON_HAS_CXX11_RVALUE_REFS -DRAPIDJSON_HAS_CXX11_...
1.	<eof> parser at end of file
2.	../../src/lib/fxl/observer_list.h:193:54: instantiating function definition 'fxl::ObserverListBase<zxdb::SettingStoreObserver>::Iter<const fxl::ObserverListBase<zxdb::SettingStoreObserver>>::~Iter'
#0 0x000055e06ddeea18 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (../../prebuilt/third_party/clang/custom/bin/clang+++0x9164a18)
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Fuchsia clang version 21.0.0git (https://llvm.googlesource.com/llvm-project 1cf9f764ac41fb3492e10c78640dd50e616388db)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: ../../prebuilt/third_party/clang/custom/bin
Build config: +assertions
clang++: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: clang-crashreports/map_setting_store-0b592c.cpp
clang++: note: diagnostic msg: clang-crashreports/map_setting_store-0b592c.sh
clang++: note: diagnostic msg:

********************
```

Could this be fixed in a timely fashion? I'll kick off a revert trial run to make sure this is the culprit.

https://luci-milo.appspot.com/ui/p/fuchsia/builders/ci/clang_toolchain.ci.core.x64-debug/b8717549930672410881/overview

https://github.com/llvm/llvm-project/pull/134038