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
diff --git a/libcxx/benchmarks/ordered_set.bench.cpp b/libcxx/benchmarks/ordered_set.bench.cpp
index e179aac..a9d9c92 100644
--- a/libcxx/benchmarks/ordered_set.bench.cpp
+++ b/libcxx/benchmarks/ordered_set.bench.cpp
@@ -14,7 +14,7 @@
 #include <string>
 #include <vector>
 
-#include "CartesianBenchmarks.hpp"
+#include "CartesianBenchmarks.h"
 #include "benchmark/benchmark.h"
 #include "test_macros.h"