preprocessor: Teach traditional about has_include [PR95889]

Traditional cpp (used by fortran) didn;t know about the new
__has_include__ implementation.  Hey, since when did traditional cpp
grow __has_include__? That wasn't in knr!

	libcpp/
	* init.c (builtin_array): Add xref comment.
	* traditional.c (fun_like_macro): Add HAS_INCLUDE codes.
	gcc/testsuite/
	* c-c++-common/cpp/has-include-1-traditional.c: New.