Fix --enable-offload-targets/-foffload handling, pt. 1

Fix --enable-offload-targets/-foffload handling, pt. 1

	gcc/
	* configure.ac (offload_targets, OFFLOAD_TARGETS): Separate
	offload targets by commas, not colons.
	* config.in: Regenerate.
	* configure: Likewise.
	* gcc.c (driver::maybe_putenv_COLLECT_LTO_WRAPPER): Due to that,
	instead of setting up the default offload targets here...
	(process_command): ..., do it here.
	libgomp/
	* plugin/configfrag.ac (OFFLOAD_TARGETS): Clarify that offload
	targets are separated by commas.
	* config.h.in: Regenerate.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@228053 138bc75d-0d04-0410-961f-82ee72b054a4