Merge pull request swiftlang#35324 from zoecarver/cxx/benchmark-header-guards

[nfc] Add header guards and "requres cplusplus" to C++ benchmarks.

Author: zoecarver

benchmark/utils/CxxTests/CreateObjects.h

@@ -1,3 +1,8 @@
+#ifndef BENCHMARK_CREATE_OBJECTS_H
+#define BENCHMARK_CREATE_OBJECTS_H
+
 struct CxxLoadableIntWrapper {
   int value;
 };
+
+#endif // BENCHMARK_CREATE_OBJECTS_H

benchmark/utils/CxxTests/module.modulemap

@@ -1,3 +1,4 @@
 module CxxCreateObjects {
   header "CreateObjects.h"
+  requires cplusplus
 }