Fix for mac

mysys/stacktrace.c

@@ -42,13 +42,16 @@ extern char *__bss_start;
 #define PTR_SANE(p) (p)
 #endif /* __linux */
 
-#ifdef __linux__
 
 void my_init_stacktrace()
 {
+#ifdef __linux__
   heap_start = (char*) &__bss_start;
+#endif /* __linux */
 }
 
+#ifdef __linux__
+
 static void print_buffer(char *buffer, size_t count)
 {
   const char s[]= " ";