Fixed nasm detection for newer autotools

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%403954

configure.in

@@ -727,7 +727,7 @@ CheckNASM()
     dnl Mac OS X might report itself as "i386" but generate x86_64 code.
     dnl  So see what size we think a pointer is, and bail if not 32-bit.
     AC_CHECK_SIZEOF([void *], 4)
-    if test x"$SIZEOF_VOID_P" != x4; then
+    if test x$ac_cv_sizeof_void_p != x4; then
         return
     fi