Various cleanups to help compile server.

	* line-map.c (add_line_map):  Allow leaving the outermost file.
	Allowing entering an outermost-file after the initial time.

	* toplev.c (pop_srcloc):  Allow popping from initial file.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@64616 138bc75d-0d04-0410-961f-82ee72b054a4