build-llvm: Bump to llvmorg-14.0.0-rc1

Notable changes include:

- LLVM can be configured to prefer forward slashes on Windows, avoiding
  the need to manually filter the Clang output in a wrapper for some
  commands.
- New Clang options for silencing warnings about unused arguments,
  avoiding the need to turn off the warning altogether. This makes
  llvm-mingw produce warnings about unused arguments among the user
  provided arguments, which never were seen before.
- Improvements to building libunwind/libcxxabi/libcxx, allowing
  simplifying the build a lot.

- Fixed generated calls to support routines for converting 128 bit integers
  from/to floats on x86_64.
- Fixed the -m32 flag, to let it figure out the right i386/arm
  architecture variant (where it previously looked for a sysroot named
  e.g. i386-*, which wasn't found).
- Fixed code generation for AArch64 in large object files (over 1 MB of
  code), where relocations against temporary symbols (jump tables,
  constant pools etc) were broken.
- Fixed continuing from breakpoints and singlestepping in LLDB on
  ARM/AArch64
- Fixed unwind info for overridden weak symbols (e.g. if overriding
  operator new with a statically linked libc++, and unwinding an exception
  through the operator).
- Set proper COFF symbol types for function aliases (e.g. for some C++
  constructors), making GNU ld export all of the correctly as the right
  type, when linking a DLL.
- Improved code generation for ARM, by assuming less strict alignment
  requirements for some instructions.

build-llvm.sh

@@ -16,7 +16,7 @@
 
 set -e
 
-: ${LLVM_VERSION:=llvmorg-13.0.0}
+: ${LLVM_VERSION:=llvmorg-14.0.0-rc1}
 ASSERTS=OFF
 unset HOST
 BUILDDIR="build"