or1k: set wchar_t to unsigned

or1k-linux-gcc defines this to be unsigned,
while or1k-elf-gcc defines it to int.
Need to investigate this, but lets follow or1k-linux-gcc for
now.
or1k: add missing pieces to thread/or1k

__unmapself.s was already added in:
9463156826d308c600f5bc013d3adb09c8825a94
or1k: add __unmapself