[Bug libgcc/122275] [16 regression] `DFP_SET_ROUNDMODE` etc. pass wrong operand size on i686-w64-mingw32 since r16-4276-g3dcf3410a74386

[lh_mouse at 126 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122275

--- Comment #3 from LIU Hao <lh_mouse at 126 dot com> ---
Created attachment 62553
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=62553&action=edit
proposed fix

So, define an `unsigned short` for x87 CW, instead of reusing `_cw` which is
exclusively used for MXCSR now.