[llgo] add USES_TERMINAL option to check-libgo

Summary:
The check-libgo target runs "make check" in the
libgo package, which can take a long time on
slower machines. To prevent buildbot failures
due to timeout, we can use Ninja's console pool
for this target.

Reviewers: pcc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9495

llvm-svn: 264815