--with-gcc-toolchain configure option breaks driver tests

I've noticed that after configuring Clang using --with-gcc-toolchain,
three driver tests fail: Driver/constructors.c,
Driver/linux-header-search.cpp, and Driver/linux-ld.c. My GCC install
is at version 4.6.3.

I looked at the Driver/constructors.c test. The problem was that the
test expected the driver to find a GCC 4.7.0 install and pass
-fuse-init-array to the compiler, but since my --with-gcc-toolchain
path pointed to a 4.6.3 install, the -fuse-init-array option was
missing.

I noticed that the tests all pass if I ensure that every RUN block has
a -gcc-toolchain option:

// RUN: -gcc-toolchain '' \

I'm seeing these failures with a recent commit on the 3.2 branch. I
also see the linux-header-search.cpp and linux-ld.c failures on 3.1.

Is this a bug in the tests?

Thanks,
-Ryan