uClibc: Always enable PTHREADS_DEBUG_SUPPORT

uClibc: Always enable PTHREADS_DEBUG_SUPPORT
This will make sure we always have the uclibc-thread-db package, which
task-sdk-bare requires.  After an audit of the versions in question, what
always happens now is that all libpthread debugging stuff from libpthread
ends up in a specific file and package.

Acked-by: Koen Kooi <koen@openembedded.org>
Acked-by: Khem Raj <raj.khem@gmail.com>
Acked-by: Leon Woestenberg <leon@sidebranch.com>
Signed-off-by: Tom Rini <trini@embeddedalley.com>