Adapted from [check_invalid_gs](https://gitlab.winehq.org/wine/wine/-/blob/d7a7cae2e2d1ad34af6dbefcb06fbef2f...) in signal_i386.c. This prevents crashing when the %gs register is manipulated in 32-bit code on "new-style" WoW64.
[test.c](https://bugs.winehq.org/attachment.cgi?id=77444) is a simple reproduction of the crash, courtesy of Fabian Maurer from the Bugzilla comments.
Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=57444
-- v3: ntdll: Check for invalid %gs value in 32-bit code on WoW64.