Fixes for glibc 2.17.

linux-os.c is just a missing header (for personality()).

In x86-64-linux-os.c, __USE_GNU is a glibc-internal name that features.h
defines; _GNU_SOURCE is what it should actually be using to get GNU extensions.

diff -x config.log -x config.status -ru tmp/sbcl-1.1.2/src/runtime/linux-os.c work/sbcl-1.1.2/src/runtime/linux-os.c
--- tmp/sbcl-1.1.2/src/runtime/linux-os.c	2012-12-01 11:32:38.000000000 +0000
+++ work/sbcl-1.1.2/src/runtime/linux-os.c	2012-12-31 01:20:37.619000000 +0000
@@ -46,6 +46,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <linux/version.h>
+#include <sys/personality.h>
 
 #include "validate.h"
 #include "thread.h"
diff -x config.log -x config.status -ru tmp/sbcl-1.1.2/src/runtime/x86-64-linux-os.c work/sbcl-1.1.2/src/runtime/x86-64-linux-os.c
--- tmp/sbcl-1.1.2/src/runtime/x86-64-linux-os.c	2012-12-01 11:32:38.000000000 +0000
+++ work/sbcl-1.1.2/src/runtime/x86-64-linux-os.c	2012-12-31 01:20:25.450000000 +0000
@@ -14,6 +14,9 @@
  * files for more information.
  */
 
+/* This is to get REG_RAX etc. from sys/ucontext.h. */
+#define _GNU_SOURCE
+
 #include <stdio.h>
 #include <stddef.h>
 #include <sys/param.h>
@@ -21,11 +24,7 @@
 #include <sys/types.h>
 #include <unistd.h>
 #include <errno.h>
-
-#define __USE_GNU
 #include <sys/ucontext.h>
-#undef __USE_GNU
-
 
 #include "./signal.h"
 #include "os.h"