msan: fix compiler warnings about unused variables


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@191821 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/msan/msan_interceptors.cc b/lib/msan/msan_interceptors.cc
index 0d5c848..b4078ad 100644
--- a/lib/msan/msan_interceptors.cc
+++ b/lib/msan/msan_interceptors.cc
@@ -1130,6 +1130,7 @@
   if (msan_init_is_running) return REAL(func)(__VA_ARGS__);   \
   MSanInterceptorContext msan_ctx = {IsInInterceptorScope()}; \
   ctx = (void *)&msan_ctx;                                    \
+  (void)ctx;                                                  \
   InterceptorScope interceptor_scope;                         \
   ENSURE_MSAN_INITED();
 #define COMMON_INTERCEPTOR_FD_ACQUIRE(ctx, fd) \