Mark unused parameters and set -Wunused-parameter

This allows us to compile with -Wall -Werror in build
environments where -Wall also warns about unused parameters.
Also explicitly set -Wunused-parameter so unused parameters will
cause the build to fail in environments where -Wall does not warn
about them.

Change-Id: Icccf2121d2a9df77b1c224c4976cb9aec56496b3
diff --git a/logging.c b/logging.c
index f2f3d50..c90b1cf 100644
--- a/logging.c
+++ b/logging.c
@@ -42,12 +42,14 @@
  * fmt  - printf format specifier
  * ...  - printf format arguments
  */
-void logmsg_dbg(int prio, const char *fmt, ...) {
 #if CLAT_DEBUG
+void logmsg_dbg(int prio, const char *fmt, ...) {
   va_list ap;
 
   va_start(ap, fmt);
   __android_log_vprint(prio, "clatd", fmt, ap);
   va_end(ap);
-#endif
 }
+#else
+void logmsg_dbg(__attribute__((unused)) int prio, __attribute__((unused)) const char *fmt, ...) {}
+#endif