This checks if gcc-go-tools have been specified in host deps
and if so, use gccgo to build (gcc-go-tools conflicts with go).
Also, since gccgo is not a multi-compiler, we need to override GCCGO
to get cross-builds. The gccgo for target is always installed, as
it's a part of our cross-toolchains.
[ci skip]
1b2bf53e82