Make test/Driver/biarch.c use FileCheck instead of grep

Summary:
For clarity and ease of maintenance, I suggest porting this test
to use the same tooling as the rest of the tests.

Reviewers: joerg, rengolin, dougk, yaron.keren

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D14548

llvm-svn: 252720