Roll gofrontend to a6e10414311a

This takes us to Go 1.4. Also includes a couple of changes to the test
suite, both in the runtime package:

- Disable TestSetPanicOnFault. We cannot support this scenario at all,
  due to LLVM's lack of non-call exceptions.

- Tweak TestFinalizerType. This test only passes with two GC runs.

Differential Revision: http://reviews.llvm.org/D8828

llvm-svn: 234134
GitOrigin-RevId: 93c73ebcbd73f5436d13ffc41f49a86fc062deb8