sleep.c doesn't compile on platforms without a clock function

git-svn-id: svn://svn.cc65.org/cc65/trunk@2218 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/common/sleep.c

@@ -13,12 +13,15 @@
 
 
 
+/* We cannot implement this function without a working clock function */
+#if defined(CLOCKS_PER_SEC)
 unsigned __fastcall__ sleep (unsigned wait)
 {
     clock_t goal = clock () + ((clock_t) wait) * CLOCKS_PER_SEC;
     while ((long) (goal - clock ()) > 0) ;
     return 0;
 }
+#endif