Fix "use of" uninitialized memory in benchmark.

An argument to DoNotOptimize was not fully initialized, which caused
msan to complain.

llvm-svn: 346808
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 9039b6012e2c18416aad0edae548c28159e12f8a
diff --git a/benchmarks/function.bench.cpp b/benchmarks/function.bench.cpp
index 484d197..4f0e1fd 100644
--- a/benchmarks/function.bench.cpp
+++ b/benchmarks/function.bench.cpp
@@ -48,7 +48,7 @@
 
 struct S {
   int function() const { return 0; }
-  int field;
+  int field = 0;
 };
 
 int FunctionWithS(const S*) { return 0; }