10l: Add useless backslashes in AltiVec CFLAGS test.

Originally committed as revision 13553 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1530,8 +1530,8 @@ fi
 
 # AltiVec flags: The FSF version of GCC differs from the Apple version
 if enabled altivec; then
-    check_cflags -maltivec -mabi=altivec &&
-        check_header altivec.h ||
+    check_cflags -maltivec -mabi=altivec && \
+        check_header altivec.h || \
         check_cflags -faltivec
 
     # check if our compiler supports Motorola AltiVec C API