Update cpuinfo.h: add support for Windows ARM64EC

[snnn]

To fix a build error:

src\arm\windows\init-by-logical-sys-info.c(309,17): Error C2065: 'cpuinfo_uarchs': undeclared identifier

In short, Arm64EC is a new application binary interface (ABI) for apps running on Arm devices with an x64 like ABI.

Reference:

1. VC++ predefined-macros
2. ARM64EC overview