adb: syntax_error: add compile time format string checking

Test: mma

Change-Id: I8eccd17a1feac0dd98fb317d30ab27489b803669
Signed-off-by: Spencer Low <CompareAndSwap@gmail.com>
diff --git a/adb/adb_utils.h b/adb/adb_utils.h
index f764a0e..f6ce8e2 100644
--- a/adb/adb_utils.h
+++ b/adb/adb_utils.h
@@ -24,7 +24,7 @@
 
 #include <android-base/macros.h>
 
-int syntax_error(const char*, ...);
+int syntax_error(const char*, ...) __attribute__((__format__(__printf__, 1, 2)));
 
 void close_stdin();