* c-common.c (combine_strings): Complain if concatenating
	__FUNCTION__.
	* c-parse.in (yylexname): Flag artificial strings.
	* tree.h (TREE_ARTIFICIAL_STRING_P): New.
doc:
	* extend.texi: Update.
testsuite:
	* gcc.dg/concat.c: New test.

From-SVN: r47890