This reverts 4d10c1165442cbbbc0017b48fcdd7dae1ccf3678 and its two
dependent commits: e6b9805b574bb5c90263ec7fbcb94df76d2807a4 and
c243406a695ca056a07ef4064b0f9feee7685320, see discussion in
https://github.com/llvm/llvm-project/pull/165598#issuecomment-3563825509.

d076608d58d1ec55016eb747a995511e3a3f72aa moved some deps around to avoid
cycles and left clang/Frontend/FrontendDiagnostic.h as a shim that
simply includes clang/Basic/DiagnosticFrontend.h. This PR inlines it so
that nothing in tree still includes clang/Frontend/FrontendDiagnostic.h.

Doing this will help prevent future layering issues. See #162865.

Frontend already depends on Basic, so no new deps need to be added
anywhere except for places that do strict dep checking.

MSVC supports an extension allowing to delete an array of objects via
pointer whose static type doesn't match its dynamic type. This is done
via generation of special destructors - vector deleting destructors.
MSVC's virtual tables always contain a pointer to the vector deleting
destructor for classes with virtual destructors, so not having this
extension implemented causes clang to generate code that is not
compatible with the code generated by MSVC, because clang always puts a
pointer to a scalar deleting destructor to the vtable. As a bonus the
deletion of an array of polymorphic object will work just like it does
with MSVC - no memory leaks and correct destructors are called.

This patch will cause clang to emit code that is compatible with code
produced by MSVC but not compatible with code produced with clang of
older versions, so the new behavior can be disabled via passing
-fclang-abi-compat=21 (or lower).

This is yet another attempt to land vector deleting destructors support
originally implemented by
https://github.com/llvm/llvm-project/pull/133451.

This PR contains fixes for issues reported in the original PR as well as
fixes for issues related to operator delete[] search reported in several
issues like

https://github.com/llvm/llvm-project/pull/133950#issuecomment-2787510484
https://github.com/llvm/llvm-project/issues/134265

Fixes https://github.com/llvm/llvm-project/issues/19772

- Fixes https://github.com/llvm/llvm-project/issues/163369
- Segmentation fault occurred because resolver was calling TSan
instrumentation functions (__tsan_func_entry, __tsan_func_exit) but as
the resolver is run by the dynamic linker at load time, TSan is not
initialized yet so the current thread pointer is null.
- This PR adds the DisableSanitizerInstrumentation attribute to the
multiversion function resolvers to avoid issues like this.
- Added regression test for TSan segfault.

This patch adds a new `FramePointerKind::NonLeafNoReserve` and makes it
the default for `-momit-leaf-frame-pointer`.

It also adds a new commandline option `-m[no-]reserve-frame-pointer-reg`.

This should fix #154379, the main impact of this patch can be found in
`clang/lib/Driver/ToolChains/CommonArgs.cpp`.

The loop iterates once and returns the first element.
Replace it with "if !empty()" to make it more explicit.

Follow up to https://github.com/llvm/llvm-project/pull/158193.

Reverts llvm/llvm-project#164432

Breaks Comgr tests with the following:


[2025-11-03T19:18:20.564Z] + clang -x hip --offload-arch=amdgcnspirv
-nogpulib -nogpuinc --no-gpu-bundle-output --offload-device-only -O3
/jenkins/workspace/compiler-psdb-amd-staging/repos/llvm-project/amd/comgr/test-lit/spirv-tests/spirv-to-reloc.hip
-o
/jenkins/workspace/compiler-psdb-amd-staging/repos/out/ubuntu-22.04/22.04/build/amd_comgr/test-lit/spirv-tests/Output/spirv-to-reloc.hip.tmp.spv
-fvisibility=hidden -fno-autolink -fexceptions -fcolor-diagnostics

[2025-11-03T19:18:20.564Z] InvalidModule: Invalid SPIR-V module: Casts
from private/local/global address space are allowed only to generic

[2025-11-03T19:18:20.564Z] 

[2025-11-03T19:18:20.564Z] <badref> = addrspacecast ptr addrspace(1)
@__hip_cuid_94fb83be5559070 to ptr

[2025-11-03T19:18:20.564Z] clang: error: amdgcn-link command failed with
exit code 10 (use -v to see invocation)

By convention the AS of the elements of `llvm.compiler.used` &
`llvm.used` is 0. However, the AS of `CGM.Int8PtrTy` is not always 0.

This leaves some LLVM helpers
(`appendToUsed/appendToCompilerUsed/removeFromUsedLists`) unusable.

This patch makes the AS of the elements of these variables to be 0.

This PR is related to https://github.com/llvm/llvm-project/pull/162660

Since pauthtest is a Linux-specific ABI, it should not be handled in
common driver code.

Module flag is used to indicate the feature to be propagated to the
function. As now the frontend emits all attributes accordingly let's
help the auto upgrade to only do work when old and new bitcodes are
merged.

Depends on #82819 and #86031