Fix search path in intelmic-mkoffload for empty COLLECT_GCC.

Fix search path in intelmic-mkoffload for empty COLLECT_GCC.

gcc/
	* config/i386/intelmic-mkoffload.c: Include intelmic-offload.h instead
	of libgomp-plugin.h.
	(find_target_compiler): Support a case when the path to gcc is specified
	in the PATH env var, so COLLECT_GCC doesn't contain a path.
	(generate_host_descr_file): Use GOMP_DEVICE_INTEL_MIC from
	intelmic-offload.h instead of OFFLOAD_TARGET_TYPE_INTEL_MIC from
	libgomp-plugin.h.
	(main): Use GCC_INSTALL_NAME as target_driver_name.
	* config/i386/t-intelmic (CFLAGS-mkoffload.o): Add GCC_INSTALL_NAME
	define.
	(mkoffload.o): Remove obsolete include path and defines.
	(mkoffload$(exeext)): Use $(LINKER) instead of $(COMPILER).

From-SVN: r221319