Don't consider '-foffload-abi' in 'DEF_GOACC_BUILTIN', 'DEF_GOMP_BUILTIN'

Don't consider '-foffload-abi' in 'DEF_GOACC_BUILTIN', 'DEF_GOMP_BUILTIN'

Since Tom's PR64707 commit r220037 (Git commit
1506ae0e1e865fb7a42fc37a47f1799b71f21c53) "Make fopenmp an LTO option" as well
as PR64672 commit r220038 (Git commit a0c88d0629a33161add8d5bc083f1e59f3f756f7)
"Make fopenacc an LTO option", we're now actually passing
'-fopenacc'/'-fopenmp' to the 'mkoffload's, which will pass these on to the
offload compilers.

	gcc/
	* builtins.def (DEF_GOACC_BUILTIN, DEF_GOMP_BUILTIN): Don't
	consider '-foffload-abi'.
	* common.opt (-foffload-abi): Remove 'Var', 'Init'.
	* opts.c (common_handle_option) <-foffload-abi> [ACCEL_COMPILER]:
	Ignore.