nios2-linux: add missing cpp specs

Define CPP_SPEC for nios2 linux targets so that -posix & -pthread work
like on all other linux targets.

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

From-SVN: r223823

gcc/ChangeLog

 2015-05-28  Mike Frysinger  <vapier@gentoo.org>
 
+	* config/nios2/linux.h (CPP_SPEC): Define.
+
+2015-05-28  Mike Frysinger  <vapier@gentoo.org>
+
 	* config/microblaze/linux.h (CPP_SPEC): Define.
 
 2015-05-28  Mike Frysinger  <vapier@gentoo.org>

gcc/config/nios2/linux.h

@@ -26,6 +26,9 @@
     }                                           \
   while (0)
 
+#undef CPP_SPEC
+#define CPP_SPEC "%{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}"
+
 #define GLIBC_DYNAMIC_LINKER "/lib/ld-linux-nios2.so.1"
 
 #undef LINK_SPEC