A workaround for go-bootstrap on x86 means we can build go proper.
Note that go also needs the same workaround.

no-pic: This is needed for building go executables on Alpine which
uses the external linker (cgo). Examples from our tree include
docker, consul and gogs. Go does not support compiling PIC executables.
Since the gcc specs used by Alpine enables PIC by default it has to be
disabled. Without disabling PIC the executable gets a ton of erroneous
textrels which results in a segfault when musl tries to resolve them.

 _SC_GETPW_R_SIZE_MAX: since musl defines this to -1 we have to
 provide a default value. Use a more recent patch from upstream which
 will be available in Go 1.6.

Also install go and gofmt binary to /usr/lib/go/bin and symlink it to
/usr/bin. Also fix removal of tests.

This might still need some further testing, especially cgo wasn't tested
to extensively by me.

The cross subpackages ships cross compilers for Darwin, FreeBSD, OpenBSD
and Microsoft Windows. Those are not all platforms theoretically
supported by go but I guess those are the most relevant once.

In the future it might be a good idea to add cross compilers for other
platforms and architectures as well but before doing so you probably
want to create one subpackage for each platform otherwise the cross
subpackage gets too big.

My computer is too slow to compile go for all these platforms and
architectures in a timely manner so I only compiled the go cross
compiler for OpenBSD amd64 and OpenBSD i386. In addition to that the
OpenBSD amd64 cross compiler was successfully used to cross compile a
small program.

If you have access to a faster computer then please test this on other
architectures (Darwin, FreeBSD and Microsoft Windows).