Update llvm-libc from LLVM 21.1.8 to 22.1.8

[aheejin]

This updates llvm-libc from 2l.1.8 to LLVM 22.1.8:
https://github.com/llvm/llvm-project/releases/tag/llvmorg-22.1.8

Additional changes:

• Exclude more files using mbstate_t: 76f80f4
  We are already excluding some files because the overlay mode doesn't support mbstate_t. There are new files using this and also some file have moved to src/stdlib. This adds those files to the excludes list.

• Exclude more files using locale_t: 90f338b
  We are already excluding some file patterns using locale_t in update_llvm_libc.py. This adds more new files to it.

• Add llvmlibc test mode to runner.py: 58736a9
  We have llvmlibc test mode in test_core.py but not in runner.py. Adds this to misc_test_modes.

All tests pass with

./test/runner llvmlibc

[aheejin]

One thing that's inconsistent is we have two different way of excluding files. float16 and locale_t-related files are excluded when copying files in update_llvm_libc.py,

emscripten/system/lib/update_llvm_libc.py

Lines 38 to 45 in 91f0234

	libc_exclusion_patterns = [
	# float16 is unsupported in Emscripten.
	'src/complex/**/*f16*',
	'src/math/generic/*f16*',
	'src/setjmp/**/*', # setjmp in Emscripten is implemented by the clang backend.
	'src/strings/str*casecmp_l*', # locale_t is unsupported in Overlay Mode.
	]

while mbstate_t-related files are copied normally but excluded in build in system_libs.py:

emscripten/tools/system_libs.py

Lines 1049 to 1050 in 91f0234

	# Overlay mode doesn't support mbstate_t which is used by these wchar sources.
	files += glob_in_path('system/lib/llvm-libc/src/wchar', '*.cpp', excludes={'wcrtomb.cpp', 'mbrtowc.cpp', 'wctomb.cpp', 'mbtowc.cpp'})

I just followed the existing methods here, but in case you think it's better to be consistent, I can use one or the other in a followup.

[sbc100]

This should probably say see the libc files?

[aheejin]

Fixed