Fix <wctype.h>.

* Fix the return type of towlower_l/towupper_l.
* Implement wctrans/wctrans_l/towctrans/towctrans_l.
* Move declarations that POSIX says are available from both <wchar.h> and
  <wctype.h> to <bits/wctype.h> and include from both POSIX headers.
* Write the missing tests.

Change-Id: I3221da5f3d7e8a2fb0a7619dc724de45f7b55398
diff --git a/tests/Android.mk b/tests/Android.mk
index 8e190ea..2db1cda 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -129,6 +129,7 @@
     unistd_test.cpp \
     utmp_test.cpp \
     wchar_test.cpp \
+    wctype_test.cpp \
 
 libBionicStandardTests_cflags := \
     $(test_cflags) \