Handle _BSD_WCHAR_T_ like _WCHAR_T_, since at least BSD/386 1.1 uses the former instead of the latter.

Handle _BSD_WCHAR_T_ like _WCHAR_T_, since at least BSD/386 1.1 uses
the former instead of the latter.  If _BSD_RUNE_T_ is defined, then
define rune_t when we define wchar_t.  Test definedness of _GCC_SIZE_T
as well as _GCC_SIZE_T_; likewise for _GCC_PTRDIFF_T and _GCC_WCHAR_T.

From-SVN: r7844