re PR preprocessor/33919 (__BASE_FILE__ does not expand correctly when included from the command line)

libcpp/
	PR preprocessor/33919
	* files.c (_cpp_get_file_name): New. Implement file name
	access function.
	* internal.h (_cpp_get_file_name): New prototype.
	* macro.c (_cpp_builtin_macro_text): Call _cpp_get_file_name()
	to use pfile->main_file in lieu of traversing INCLUDED_FROM chain.

gcc/testsuite/
	PR preprocessor/33919
	* gcc.dg/pr33919.c: New test.
	* gcc.dg/pr33919-0.h: New test header file.
	* gcc.dg/pr33919-1.h: Ditto.
	* gcc.dg/pr33919-2.h: Ditto.

From-SVN: r183003