add configure.in support for MMX instruction compiler intrinsics

configure.in

@@ -1621,6 +1621,9 @@ AC_CHECK_HEADERS(X11/XKBlib.h)
 dnl These are all the places some variant of statfs can be hiding.
 AC_CHECK_HEADERS(sys/statvfs.h sys/statfs.h sys/vfs.h sys/mount.h)
 
+dnl Try for MMX support
+AC_CHECK_HEADERS(mmintrin.h)
+
 dnl Check whether the compiler supports the new-style C++ standard
 dnl library headers (i.e. <new>) or needs the old "new.h"
 AC_LANG_CPLUSPLUS