microblaze-linux: add missing cpp specs

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

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

From-SVN: r223822

gcc/ChangeLog

 2015-05-28  Mike Frysinger  <vapier@gentoo.org>
 
+	* config/microblaze/linux.h (CPP_SPEC): Define.
+
+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.
 

gcc/config/microblaze/linux.h

@@ -22,6 +22,9 @@
 #undef TARGET_SUPPORTS_PIC
 #define TARGET_SUPPORTS_PIC 1
 
+#undef CPP_SPEC
+#define CPP_SPEC "%{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}"
+
 #undef TLS_NEEDS_GOT
 #define TLS_NEEDS_GOT 1