Add arm64ec support on Visual Studio

Hi,


Arm64ec is an architecture supported on Windows 11. In short, it runs 
smooth on arm64 processors without emulation, but it is compatible with 
x64. So you can load arm64ec dll's in x64 processes and vise versa, as 
long as you're on an arm64 host system.

It is already possible to compile arm64ec on SCons by adding /ARM64EC to 
ccflags and /machine:arm64ec to linkflags. However I think it would be 
better to add arm64ec as a supported architecture directly in SCons 
itself, and it should append to ccflags and linkflags itself.

Would you be open for a pull request that adds this?


Cheers,


Leoanrd