hppa-linux: add missing cpp specs

Define CPP_SPEC for parisc linux targets so that -posix & -pthread work
like on all other linux targets.

Discovered via Gentoo bug https://bugs.gentoo.org/543114

From-SVN: r223820

gcc/ChangeLog

+2015-05-28  Mike Frysinger  <vapier@gentoo.org>
+
+	* config/pa/pa-linux.h (CPP_SPEC): Change so -D_REENTRANT is used when
+	-pthread is specified.
+
 2015-05-28  Richard Biener  <rguenther@suse.de>
 
 	* tree-vect-loop.c (vect_fixup_reduc_chain): New function.

gcc/config/pa/pa-linux.h

@@ -28,7 +28,7 @@ along with GCC; see the file COPYING3.  If not see
   while (0)
 
 #undef CPP_SPEC
-#define CPP_SPEC "%{posix:-D_POSIX_SOURCE}"
+#define CPP_SPEC "%{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}"
 
 #undef ASM_SPEC
 #define ASM_SPEC \