CMake: Fix Windows exceptions flag
This commit changes the exception flag to match the description and turn
off exceptions. This matches the behavior of -fno-exceptions. However,
on Windows SEH exceptions are always available, and there's no easy way
to turn them off. This flag should also suppress previous /EHsc flags,
if they get automatically set by cmake. Reference:
https://learn.microsoft.com/en-us/cpp/build/reference/eh-exception-handling-model?view=msvc-170