Running llvmgcc only (under test/Programs)

Since we only have a Solaris version of the front-end (llvmgcc),
we need to compile .c -> .ll files on a solaris machines in
order to run the tests in Programs/. Doing this manually for
all the C source files is really difficult.

I added a flag called RUN_GCC_ONLY in test/Programs/Makefile.programs
that will cause gmake to run only llvmgcc. Run the following in
test/Programs to build .ll files for all the C source files. After that
you can run the rest of the tests under Linux as before:

  gmake RUN_GCC_ONLY=1