Fix tracing in libts

Libts deployments did not include posix_trace.c in the build and as
a result setting TRACE_LEVEL to any value above TRACE_LEVEL_NONE
resulted in a build error.

- Add the missing C file to the build to fix this error.
- Make the arm-linux version of libts to implement tracing
the same way as linux-pc.

Change-Id: I1db6117a0e8aa4955de063e7b22618d4a254973f
Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
8 files changed