test-suite: Added new test suite feature (experimental)

This patch adds support for installing the gcc test suite. A helper
Makefile is provided for building and running the gcc tests.

The default configuration runs all gcc tests and requires automatic
ssh/scp login access to a networked target board. See README for
more details.

Note: Current feature is tested with the powerpc-unknown-linux-gnu
sample but it should work with others as well.

Signed-off-by: Martin Lund <mgl@doredevelopment.dk>

 # Dummy config file to not use a C library *at all*

 # depends on BARE_METAL

 config LIBC_none

     help

       Do not use a C library.

       This is usefull if your project is self-contained, does not rely on

       an external C library, and provides all the necessary bits.

       Most probably usefull to bootloaders, as they generally don't depend

       on the C library.

       If unsure: do *not* choose that, and use another option in the choice.