tree-wide: replace MAYBE_UNUSED with ASSERTED

Suggested-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/util/macros.h

@@ -230,13 +230,30 @@ do {                       \
 #  endif
 #endif
 
+/**
+ * UNUSED marks variables (or sometimes functions) that have to be defined,
+ * but are sometimes (or always) unused beyond that. A common case is for
+ * a function parameter to be used in some build configurations but not others.
+ * Another case is fallback vfuncs that don't do anything with their params.
+ *
+ * Note that this should not be used for identifiers used in `assert()`;
+ * see ASSERTED below.
+ */
 #ifdef HAVE_FUNC_ATTRIBUTE_UNUSED
 #define UNUSED __attribute__((unused))
 #else
 #define UNUSED
 #endif
 
-#define MAYBE_UNUSED UNUSED
+/**
+ * Use ASSERTED to indicate that an identifier is unused outside of an `assert()`,
+ * so that assert-free builds don't get "unused variable" warnings.
+ */
+#ifdef NDEBUG
+#define ASSERTED UNUSED
+#else
+#define ASSERTED
+#endif
 
 #ifdef HAVE_FUNC_ATTRIBUTE_WARN_UNUSED_RESULT
 #define MUST_CHECK __attribute__((warn_unused_result))
@@ -261,7 +278,7 @@ do {                       \
  */
 #define ASSERT_BITFIELD_SIZE(STRUCT, FIELD, MAXVAL) \
    do { \
-      MAYBE_UNUSED STRUCT s;                \
+      ASSERTED STRUCT s; \
       s.FIELD = (MAXVAL); \
       assert((int) s.FIELD == (MAXVAL) && "Insufficient bitfield size!"); \
    } while (0)