Roll gotools to d4e70101.

Most importantly, this gives us https://go-review.googlesource.com/7533 which
fixes a bug in go/ssa that caused test failures in the Go 1.4 standard library.

Also remove the go1.4 tag workaround. We no longer need it now that we
ship llgo-go.

Differential Revision: http://reviews.llvm.org/D8827

llvm-svn: 234133