Better fix from Max Horn

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%403922

src/video/quartz/SDL_QuartzEvents.m

@@ -31,7 +31,13 @@
 /*
  * On Leopard, this is missing from the 64-bit headers
  */
-#ifndef UsrActivity
+#if defined(__LP64__) && !defined(__POWER__)
+/*
+ * Workaround for a bug in the 10.5 SDK: By accident, OSService.h does
+ * not include Power.h at all when compiling in 64bit mode. This has
+ * been fixed in 10.6, but for 10.5, we manually define UsrActivity
+ * to ensure compilation works.
+ */
 #define UsrActivity 1
 #endif