rt-tests: backport patch that enable build for all archs

Upstream rt-tests has applied a patch that allow builds for all archs.
The problem is that oslat using frc() that is not present for all archs.
With this backported patch oslat is building but in run-time an error
message is dumped if frc() is not present.

Signed-off-by: Peter Bergin <peter@berginkonsult.se>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>