tcg-s390: Adjust compilation flags.

Force -m31/-m64 based on s390/s390x target.

Force -march=z990.  The TCG backend will always require the
long-displacement facility, so the compiler may as well make
use of that as well.
Signed-off-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

configure

@@ -720,7 +720,12 @@ case "$cpu" in
            fi
            ;;
     s390)
-           QEMU_CFLAGS="-march=z900 $QEMU_CFLAGS"
+           QEMU_CFLAGS="-m31 -march=z990 $QEMU_CFLAGS"
+           LDFLAGS="-m31 $LDFLAGS"
+           ;;
+    s390x)
+           QEMU_CFLAGS="-m64 -march=z990 $QEMU_CFLAGS"
+           LDFLAGS="-m64 $LDFLAGS"
            ;;
     i386)
            QEMU_CFLAGS="-m32 $QEMU_CFLAGS"