ART: Fix mac build

Parameter is unused in the mac build. We now build the test libraries
in checkbuild, which exposed the issue.

Change-Id: Ib246d87927740e2e65a63111bdf0cc4f261b4c1c
diff --git a/test/137-cfi/cfi.cc b/test/137-cfi/cfi.cc
index 59722ad..78f8842 100644
--- a/test/137-cfi/cfi.cc
+++ b/test/137-cfi/cfi.cc
@@ -235,6 +235,7 @@
 
   return result ? JNI_TRUE : JNI_FALSE;
 #else
+  UNUSED(pid_int);
   return JNI_FALSE;
 #endif
 }