libiberty: sync with gcc

libiberty: sync with gcc

This imports the following commits from GCC as of r15-1722-g7682d115402743:
	ca2f7c84927f libiberty: Invoke D demangler when --format=auto
	94792057ad4a Fix up duplicated words mostly in comments, part 1
	20e57660e64e libiberty: Fix error return value in pex_unix_exec_child [PR113957].
	52ac4c6be866 [libiberty] remove TBAA violation in iterative_hash, improve code-gen
	53bb7145135c libiberty: Fix up libiberty_vprintf_buffer_size
	65388b28656d c++, demangle: Implement https://github.com/itanium-cxx-abi/cxx-abi/issues/148 non-proposal