Darwin: Check for x86_64 only on i386

The sysctl variable if we're 64-bit capable only exists on i386. So we should only check it if we're on i386.

This suppresses a warning on PowerPC spotted by Andreas Faerber.
Signed-off-by: NAlexander Graf <alex@csgraf.de>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6640 c046a42c-6fe2-441c-8c8c-71466251a162

configure

@@ -244,9 +244,9 @@ Darwin)
 bsd="yes"
 darwin="yes"
 # on Leopard most of the system is 32-bit, so we have to ask the kernel it if we can run 64-bit userspace code
-is_x86_64=`sysctl -n hw.optional.x86_64`
-if [ "$is_x86_64" = "1" ]; then
-    cpu=x86_64
+if [ "$cpu" = "i386" ] ; then
+    is_x86_64=`sysctl -n hw.optional.x86_64`
+    [ "$is_x86_64" = "1" ] && cpu=x86_64
 fi
 if [ "$cpu" = "x86_64" ] ; then
     OS_CFLAGS="-arch x86_64"