Specify reason of -Winvalid-pch warning

gcc/c-family
	PR pch/86674
	* c-pch.c (c_common_valid_pch): Use cpp_warning with CPP_W_INVALID_PCH
	reason to fix -Werror=invalid-pch and -Wno-error=invalid-pch switches.

libcpp
	PR pch/86674
	* files.c (_cpp_find_file): Use CPP_DL_NOTE not CPP_DL_ERROR in call to
	cpp_error.