Compilers that generate PIE code by default will break the tests,
since they must be fully statically linked, whereas PIE requires a
dynamic linker to relocate the images at runtime.

So, forcibly disable PIE when building.

For good measure, also pass -static when linking.  With no standard
libraries and no PIE, this should make no difference, but let's
play safe.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>