Go 1.4's runtime-gdb.py is broken, so the reason why x86 builders are
passing that test
is definitely not because they are using Go 1.4 version of runtime-gdb.py.
Something else is happening that makes the runtime path correct despite the
we set GOROOT_FINAL.
(Or it is possible that only the old style builders set GOROOT_FINAL, and
builders are not?)