Log Message:
libgpg-error: Make this cross-compile on NetBSD.

Provide an architecture-independent definition of a structure that
wraps pthread_mutex_t.  For some reason libgpg-error tries to
discover this by a runtime test in the configure script and spit out
C approximating the declaration automagically, which is incompatible
with cross-compilation.  Since PTHREAD_MUTEX_INITIALIZER always works
on NetBSD, just use that.

No change to native compilation because it always tries
`lock-obj-pub.native.h' first -- the one it generated during
configure -- and then falls back to the cross options like this patch
adds.