libcxx: Rename .hpp files in libcxx/benchmarks to .h

LLVM uses .h as its extension for header files.

Differential Revision: https://reviews.llvm.org/D66509

llvm-svn: 369487
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: f938755a331206f017eaa5e8ab6a122b162e8de3
diff --git a/benchmarks/string.bench.cpp b/benchmarks/string.bench.cpp
index 22d84af..c4f2090 100644
--- a/benchmarks/string.bench.cpp
+++ b/benchmarks/string.bench.cpp
@@ -3,8 +3,8 @@
 #include <new>
 #include <vector>
 
-#include "CartesianBenchmarks.hpp"
-#include "GenerateInput.hpp"
+#include "CartesianBenchmarks.h"
+#include "GenerateInput.h"
 #include "benchmark/benchmark.h"
 #include "test_macros.h"