uclibc: use shell script testsuite runner

uclibc: use shell script testsuite runner

There is no need for GNU make to run the testsuite.
The benefit is you can even try it on noMMU targets as
the script runs with busybox hush.
Parallel build of the testsuite seems to work well.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>