Add trivial <ctype.h> benchmarks.

Just to sanity check that toupper/tolower and towupper/towlower are in
the same ballpark for the ASCII range.

Test: ran benchmarks
Change-Id: I1ddc3f4f4478b4075107831f27bf4d4b4a3bc5e8

benchmarks/Android.bp

@@ -28,6 +28,7 @@ cc_defaults {
     srcs: [
         "bionic_benchmarks.cpp",
         "atomic_benchmark.cpp",
+        "ctype_benchmark.cpp",
         "get_heap_size_benchmark.cpp",
         "inttypes_benchmark.cpp",
         "malloc_benchmark.cpp",

benchmarks/ctype_benchmark.cpp

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <ctype.h>
+
+#include <benchmark/benchmark.h>
+#include "util.h"
+
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_tolower_y, tolower('X'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_tolower_n, tolower('x'));
+
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toupper_y, toupper('x'));
+BIONIC_TRIVIAL_BENCHMARK(BM_ctype_toupper_n, toupper('X'));