Fix -save-temp leaking files in /tmp

Fix -save-temp leaking files in /tmp

And avoid signal handler calling signal unsafe functions,
and/or calling unlink with uninitialized memory pointer.

2020-02-19  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* collect2.c (c_file, o_file): Make const again.
	(ldout,lderrout, dump_ld_file): Remove.
	(tool_cleanup): Avoid calling not signal-safe functions.
	(maybe_run_lto_and_relink): Avoid possible signal handler
	access to unintialzed memory (lto_o_files).
	(main): Avoid leaking temp files in $TMPDIR.
	Initialize c_file/o_file with concat, which avoids exposing
	uninitialized memory to signal handler, which calls unlink(!).
	Avoid calling maybe_unlink when the main function returns,
	since the atexit handler is already doing this.
	* collect2.h (dump_ld_file, ldout, lderrout): Remove.