build-llvm: Bump to LLVM 22.1.0 RC 1

Some notable changes since LLVM 21.x related to mingw:

- Handle an uncommon error code in libcxx's std::filesystem,
  avoiding spurious test failures if running the libcxx test suite
  (noted at least occasionally on Github Actions)
- Reinstate x86 stack probe functions in compiler-rt, that we earlier
  beleived weren't used - but turned out to be used by GCC in i386
  mode
- Fix interpretation of a few corner case aarch64 SEH unwind opcodes
- Support for FAT LTO (compile with -ffat-lto-objects, link with
  -Wl,--fat-lto-objects)
- llvm-objcopy: Support the -p option for COFF targets
- llvm-readobj: A new option --coff-pseudoreloc for dumping information
  and symbols for mingw runtime pseudo relocations
- Lots of various fixes for the cygwin target
- Improve linking a custom CRT with binutils ld (by passing the custom
  CRT -l option at the same place as the original default -lmsvcrt)
- Make lld use the right mingw specific DLL entry point implicitly,
  improving some Rust use cases
- Fix running the libcxx tests with optimization for mingw targets,
  allowing more test coverage of the code generation paths

build-llvm.sh

@@ -17,7 +17,7 @@
 set -e
 
 : ${LLVM_REPOSITORY:=https://github.com/llvm/llvm-project.git}
-: ${LLVM_VERSION:=llvmorg-21.1.8}
+: ${LLVM_VERSION:=llvmorg-22.1.0-rc1}
 ASSERTS=OFF
 unset HOST
 BUILDDIR="build"