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/unordered_set_operations.bench.cpp b/libcxx/benchmarks/unordered_set_operations.bench.cpp
index 1fee6d3..3824386 100644
--- a/libcxx/benchmarks/unordered_set_operations.bench.cpp
+++ b/libcxx/benchmarks/unordered_set_operations.bench.cpp
@@ -7,8 +7,8 @@
 
 #include "benchmark/benchmark.h"
 
-#include "ContainerBenchmarks.hpp"
-#include "GenerateInput.hpp"
+#include "ContainerBenchmarks.h"
+#include "GenerateInput.h"
 #include "test_macros.h"
 
 using namespace ContainerBenchmarks;