wchar_t change for ARM EABI

[Andrew Turner]

I have a patch at [1] to move the wchar_t type definition from
<sys/_types.h> to <machine/_types.h> I would like feedback on. The need
for this change is the ARM EABI requires wchar_t to be either an
unsigned int or an unsigned short, with the former preferred.

I have only made the change for ARM in the patch but if it looks
correct I will update all arch's.

Andrew

[1] http://people.freebsd.org/~andrew/wchar_unsigned.diff