Add trivial tests for fnmatch(3).

These cover the parts of fnmatch() that I think I understand. Missing
FNM_LEADING_DIR because I still haven't understood that yet. All the
descriptions of its behavior that I've seen are slightly (or very)
inconsistent, and it seems like the implementations are genuinely
different too.

Test: treehugger
Change-Id: I1284c406639bef1bfe74db3cad45965c8ab29c2b
diff --git a/tests/Android.bp b/tests/Android.bp
index a7f6229..477c8fc 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -332,6 +332,7 @@
         "fenv_test.cpp",
         "_FILE_OFFSET_BITS_test.cpp",
         "float_test.cpp",
+        "fnmatch_test.cpp",
         "ftw_test.cpp",
         "getauxval_test.cpp",
         "getcwd_test.cpp",