lock: fix compilation error on HP-UX IA64

[Bruno Haible]

On HP-UX IA64 with this new shining compiler, I'm seeing this compilation
error:

-------------------------------------------------------------------------------
cc +DD64 -AC99 -D_XOPEN_SOURCE=500 -DHAVE_CONFIG_H -I. -I../../src/gllib -I..  
-g -c -o glthread/lock.o ../../src/gllib/glthread/lock.c
"../../src/gllib/glthread/lock.h", line 143: error #4270: 
"pthread_rwlockattr_setkind_np" is undefined, pragma ignored
  #  pragma weak pthread_rwlockattr_setkind_np
  ^

1 error detected in the compilation of "../../src/gllib/glthread/lock.c".
-------------------------------------------------------------------------------

Although this error message is a candidate for a hall of fame, let me add a
workaround:


2017-03-19  Bruno Haible  <address@hidden>

        lock: Fix compilation error with HP-UX IA64 cc.
        * lib/glthread/lock.h (pthread_rwlockattr_setkind_np): Don't declare
        weak on non-glibc platforms.

diff --git a/lib/glthread/lock.h b/lib/glthread/lock.h
index 67932aa..ec8d11d 100644
--- a/lib/glthread/lock.h
+++ b/lib/glthread/lock.h
@@ -140,7 +140,9 @@ extern int glthread_in_use (void);
 #  pragma weak pthread_mutexattr_settype
 #  pragma weak pthread_mutexattr_destroy
 #  pragma weak pthread_rwlockattr_init
-#  pragma weak pthread_rwlockattr_setkind_np
+#  if __GNU_LIBRARY__ > 1
+#   pragma weak pthread_rwlockattr_setkind_np
+#  endif
 #  pragma weak pthread_rwlockattr_destroy
 #  ifndef pthread_self
 #   pragma weak pthread_self