crt: crt_handler: Enable __mingw_SEH_error_handler code for all builds

Improve __mingw_SEH_error_handler() to include also handling of __SEH__ and
non-_WIN64 code from _gnu_exception_handler() function. With this change
__mingw_SEH_error_handler() and _gnu_exception_handler() would provide same
functionality.

Signed-off-by: LIU Hao <lh_mouse@126.com>