re PR c++/17577 (#pragma implementation no longer diagnoses use after file to which it applies)

gcc/cp
	PR c++/17577:
	* lex.c (handle_pragma_implementation): Use cpp_included_before.
gcc/testsuite
	PR c++/17577:
	* g++.dg/ext/pr17577.h: New file.
	* g++.dg/ext/pr17577.C: New file.
libcpp
	PR c++/17557:
	* include/cpplib.h (cpp_included_before): Declare.
	* files.c (struct file_hash_entry) <location>: New field.
	(_cpp_find_file): Initialize new field.
	(make_cpp_dir): Likewise.
	(cpp_included_before): New function.

From-SVN: r130093