[compiler-rt] [libcxx] [llvm] compiler-rt: Introduce runtime functions for emulated PAC. (PR #133530)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

This seems to cause failures in running the compiler-rt tests on Windows on aarch64:

https://github.com/mstorsjo/llvm-mingw/actions/runs/16183738002/job/45702529351#step:8:1964

```
# executed command: not KillTheDoctor 'C:\a\llvm-mingw\llvm-mingw\llvm-project\build-compiler-rt\test\builtins\Unit\AARCH64WindowsConfig\aarch64\Output\emupac.c.tmp' 3
# note: command had no output on stdout or stderr
# error: command failed with exit status: 1
```
It doesn't seem to contain much other details about the issue, unless the compiler warnings about the size of long for printfs are related.


Separately, a build of LLVM on macOS, using the latest Clang+LLVM+compiler-rt, also seems to be failing now (but that's possibly related to another PR than this one):

https://github.com/mstorsjo/llvm-mingw/actions/runs/16183738002/job/45692829706

```
ld64.lld: error: undefined symbol for arch arm64: _emupac_pacda_impl
>>> referenced by /Users/runner/llvm/lib/clang/21/lib/darwin/libclang_rt.osx.a(emupac.cpp.o):(symbol _emupac_pacda+0x8)
>>> did you mean: __emupac_pacda_impl
>>> defined in: /Users/runner/llvm/lib/clang/21/lib/darwin/libclang_rt.osx.a(emupac.cpp.o)
```


https://github.com/llvm/llvm-project/pull/133530