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
diff --git a/benchmarks/Android.bp b/benchmarks/Android.bp
index f2ab32a..70f7bab 100644
--- a/benchmarks/Android.bp
+++ b/benchmarks/Android.bp
@@ -28,6 +28,7 @@
     srcs: [
         "bionic_benchmarks.cpp",
         "atomic_benchmark.cpp",
+        "ctype_benchmark.cpp",
         "get_heap_size_benchmark.cpp",
         "inttypes_benchmark.cpp",
         "malloc_benchmark.cpp",