Fix the use of linemap_add and remove unnecessary kludge

Fix the use of linemap_add and remove unnecessary kludge

libcpp/

	* line-map.c (linemap_add): Assert that reason must not be
	LC_RENAME when called for the first time on a "main input file".

c-family/

	* c-pch.c (c_common_read_pch): Call linemap_add with LC_ENTER as it's
	the first time it's being called on this main TU.

gcc/lto/

	* lto-lang.c (lto_init): Likewise.  Also, avoid calling
	linemap_add twice.

gcc/fortran/

	* scanner.c (load_file): Don't abuse LC_RENAME reason while
	(indirectly) calling linemap_add.

From-SVN: r178146