Makefile: Add pthreads to LIBS
Makefile: Add pthreads to LIBS

It's needed by MPS.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@kernel.org>

penberg/hornet,penberg/hornet,penberg/hornet,penberg/hornet