pthread, pthread_sigmask, threadlib: port to Ubuntu 14.04
Problem reported by Assaf Gordon in:
http://lists.gnu.org/archive/html/bug-gnulib/2014-09/msg00023.html
Apparently Ubuntu is doing some fancy link-time optimization
that doesn't work with -lpthread but does work with -pthread.
Work around the bug by preferring -pthread to -lpthread.
This change affects only LIBS, not CFLAGS, which is a little
weird, but it works.
* m4/pthread.m4 (gl_PTHREAD_CHECK):
* m4/threadlib.m4 (gl_THREADLIB_BODY): Prefer -pthread to -lpthread.
* m4/pthread_sigmask.m4 (gl_FUNC_PTHREAD_SIGMASK):
Treat -pthread like -lpthread.