If we have NetBSD 2.99.10 and higher, getpwuid_r and friends exist,
but _PTHREAD_THREAD_SAFE_FUNCTIONS might not be defined. Define it.
For NetBSD before 2.99.10, explicitly set XNO_MTSAFE_PWDAPI to enforce
locked access via normal functions.
xpkgwedge. Also, OpenMotif can actually be installed into ${LOCALBASE}
if xpkgwedge is installed. Use x11.buildlink.mk and mark as
USE_BUILDLINK_ONLY, and add a buildlink.mk file for use by other package
Makefiles.