ac-power: define main through macro

I decided to use a separate definition for this because it's too easy to return
positive from functions which don't need this distinction and only return
negative on error and success otherwise.

src/basic/macro.h

@@ -515,4 +515,14 @@ static inline int __coverity_check__(int condition) {
                 return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;             \
         }
 
+/* Zero is mapped to EXIT_SUCCESS, and both negative and positive values
+ * are mapped to EXIT_FAILURE.
+ * Note: this means "true" maps to EXIT_FAILURE. */
+#define DEFINE_MAIN_FUNCTION_WITH_POSITIVE_FAILURE(impl)                \
+        int main(int argc, char *argv[]) {                              \
+                int r;                                                  \
+                r = impl(argc, argv);                                   \
+                return r != 0 ? EXIT_FAILURE : EXIT_SUCCESS;            \
+        }
+
 #include "log.h"