Switch one other location from i386 -> x86_64 by default.

We have both config.h and llvm-config.h defining this same default
triple, but I only updated one of them in my previous change. This CL
updates the host llvm-config.h as well, so that no warnings are
generated for the mismatch.

Change-Id: I0fc30d97aca8d8ab3c66614c42733a9c0bd83373
1 file changed