src/libpcp/src/lock.c: restore debugging guard
src/libpcp/src/lock.c: restore debugging guard

Got mangled in the recent debugging control changes.  Put it back
to the same boolean expression as previously, and now magically
qa/954 is passing again.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp