ndk: Fix WCHAR_MIN / WCHAR_MAX definitions.

This fixes WCHAR_MIN / WCHAR_MAX to be signed / unsigned based on
the target ABI.

This only impacts ARM where wchar_t is really 'unsigned int'.
One can define _WCHAR_IS_ALWAYS_SIGNED to restore the old behaviour.

See http://b.android.com/55749

Change-Id: Idb63b7b11aecd3cfee37f5b6dd2eba78b308876f
5 files changed