Declare __FAKE_USE_VA_ARGS as a variadic function.

This avoids 2 static analysis warnings:
* assigned but unused variables in __VA_ARGS__
* unused expression result in __VA_ARGS__

Bug: 111614304
Test: make with WITH_TIDY=1
Change-Id: I4faae8787f6cc76de7ff4b6d08d25d0cb47324ea
diff --git a/liblog/include/log/log_main.h b/liblog/include/log/log_main.h
index f1ff31a..9c68ff2 100644
--- a/liblog/include/log/log_main.h
+++ b/liblog/include/log/log_main.h
@@ -43,10 +43,11 @@
 /*
  * Use __VA_ARGS__ if running a static analyzer,
  * to avoid warnings of unused variables in __VA_ARGS__.
+ * __FAKE_USE_VA_ARGS is undefined at link time,
+ * so don't link with __clang_analyzer__ defined.
  */
-
 #ifdef __clang_analyzer__
-#define __FAKE_USE_VA_ARGS(...) ((void)(__VA_ARGS__))
+extern void __FAKE_USE_VA_ARGS(...);
 #else
 #define __FAKE_USE_VA_ARGS(...) ((void)(0))
 #endif