Do not hardcode -m64 into the build system

--- a/configure.ac
+++ b/configure.ac
@@ -21,12 +21,12 @@
 						   [ext_CFLAGS="-arch x86_64 -arch i386 -arch ppc64 -arch ppc"],
 						   [ext_CFLAGS="-arch i386 -arch ppc"]);;
 	  0) CFLAGS="-m64"
-	  	 AC_COMPILE_IFELSE([AC_LANG_PROGRAM], [ext_CFLAGS="-m64"], []);;
+	  	 AC_COMPILE_IFELSE([AC_LANG_PROGRAM], [ext_CFLAGS=""], []);;
 	esac;;
   *)
     AC_MSG_CHECKING([if gcc accepts -m64])
     CFLAGS="-m64"
-    AC_COMPILE_IFELSE([AC_LANG_PROGRAM], [ext_CFLAGS="-m64"; AC_MSG_RESULT([yes])],
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM], [ext_CFLAGS=""; AC_MSG_RESULT([yes])],
 					  [ext_CFLAGS="-D_FILE_OFFSET_BITS=64"; AC_MSG_RESULT([no])]);;
 esac
 AC_ARG_ENABLE(experimental, [  --enable-experimental   enable experimental features],