fix clang build problem:

python3/Modules/_ctypes/libffi/src/x86/sysv.S:389:17: error: invalid variant ´rel´
Patch by: Rafael Avila de Espindola <respindola at mozilla dot com>
https://417179.bugs.gentoo.org/attachment.cgi?id=313299

diff -ru python3.old/Modules/_ctypes/libffi/configure.ac python3/Modules/_ctypes/libffi/configure.ac
--- python3.old/Modules/_ctypes/libffi/configure.ac	2012-09-29 10:00:42.000000000 +0200
+++ python3/Modules/_ctypes/libffi/configure.ac	2012-11-27 16:12:44.421564130 +0100
@@ -303,10 +303,10 @@
 if test x$TARGET = xX86 || test x$TARGET = xX86_WIN32 || test x$TARGET = xX86_64; then
     AC_CACHE_CHECK([assembler supports pc related relocs],
 	libffi_cv_as_x86_pcrel, [
-	libffi_cv_as_x86_pcrel=yes
+	libffi_cv_as_x86_pcrel=no
 	echo '.text; foo: nop; .data; .long foo-.; .text' > conftest.s
-	if $CC $CFLAGS -c conftest.s 2>&1 | $EGREP -i 'illegal|warning' > /dev/null; then
-	    libffi_cv_as_x86_pcrel=no
+	if $CC $CFLAGS -c conftest.s > /dev/null; then
+	    libffi_cv_as_x86_pcrel=yes
 	fi
 	])
     if test "x$libffi_cv_as_x86_pcrel" = xyes; then
diff -ru python3.old/Modules/_ctypes/libffi/configure python3/Modules/_ctypes/libffi/configure
--- python3.old/Modules/_ctypes/libffi/configure	2012-09-29 10:00:42.000000000 +0200
+++ python3/Modules/_ctypes/libffi/configure	2012-11-27 16:12:44.420564130 +0100
@@ -14322,10 +14322,10 @@
   $as_echo_n "(cached) " >&6
 else
 
-	libffi_cv_as_x86_pcrel=yes
+	libffi_cv_as_x86_pcrel=no
 	echo '.text; foo: nop; .data; .long foo-.; .text' > conftest.s
-	if $CC $CFLAGS -c conftest.s 2>&1 | $EGREP -i 'illegal|warning' > /dev/null; then
-	    libffi_cv_as_x86_pcrel=no
+	if $CC $CFLAGS -c conftest.s > /dev/null; then
+	    libffi_cv_as_x86_pcrel=yes
 	fi
 
 fi