gc compiler.
	-gccgoprefix prefix
		The -fgo-prefix option to be used with gccgo.
	-gccgopkgpath path
		The -fgo-pkgpath option to be used with gccgo.
	-gccgo_define_cgoincomplete
		Define cgo.Incomplete locally rather than importing it from
		the "runtime/cgo" package. Used for old gccgo versions.
	-godefs
		Write out input file in Go syntax replacing C package