go-bootstrap: add BR2_PACKAGE_HOST_GO_BOOTSTRAP_ARCH_SUPPORTS

go-bootstrap: add BR2_PACKAGE_HOST_GO_BOOTSTRAP_ARCH_SUPPORTS

go-bootstrap is a host package that builds a first stage Go compiler,
later used to build the final Go compiler. However, this first stage
compiler only supports building on x86, x86-64 and arm as host
architectures, so we need to add the relevant architecture
dependencies to avoid having go-bootstrap built on other unsupported
platforms.

We do this by introducing BR2_PACKAGE_HOST_GO_BOOTSTRAP_ARCH_SUPPORTS
in a new package/go-bootstrap/Config.in.host file. This option is then
used by BR2_PACKAGE_HOST_GO_ARCH_SUPPORTS to make sure we can't enable
Go packages when the host architecture doesn't allow building the Go
compiler.

Fixes:

  http://autobuild.buildroot.net/results/cbd419c6ab6fa8a6d18dc137c91f895867e53b8a/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>