offload-defaulted: Config option to silently ignore uninstalled offload compilers

offload-defaulted: Config option to silently ignore uninstalled offload compilers

If configured with --enable-offload-defaulted, configured but not installed
offload compilers and libgomp plugins are silently ignored.  Useful for
distribution compilers where those are in separate optional packages.

2021-04-28  Jakub Jelinek  <jakub@redhat.com>
	    Tobias Burnus  <tobias@codesourcery.com>

ChangeLog:

	* configure.ac (--enable-offload-defaulted): New.
	* configure: Regenerate.

gcc/ChangeLog:

	* configure.ac (OFFLOAD_DEFAULTED): AC_DEFINE if offload-defaulted.
	* gcc.c (process_command): New variable.
	(driver::maybe_putenv_OFFLOAD_TARGETS): If OFFLOAD_DEFAULTED,
	set it if -foffload is defaulted.
	* lto-wrapper.c (OFFLOAD_TARGET_DEFAULT_ENV): Define.
	(compile_offload_image): If OFFLOAD_DEFAULTED and
	OFFLOAD_TARGET_DEFAULT is in the environment, don't fail
	if corresponding mkoffload can't be found.
	(compile_images_for_offload_targets): Likewise.  Free and clear
	offload_names if no valid offload is found.
	* config.in: Regenerate.
	* configure: Regenerate.

libgomp/ChangeLog:

	* configure.ac (OFFLOAD_DEFAULTED): AC_DEFINE if offload-defaulted.
	* target.c (gomp_load_plugin_for_device): If set and if a plugin
	can't be dlopened, silently assume it has no devices.
	* Makefile.in: Regenerate.
	* config.h.in: Regenerate.
	* configure: Regenerate.