libobs: Restrict emmintrin.h to x86(_64) platform

There is a new toolchain called ARM64EC on MSVC which allows linking x64 objects to ARM64 objects.

It defines multiple architecture preprocessor definition including but not limited to `_M_X64`, `_M_ARM64` and `_M_ARM64EC`.

The original implementation will fail if compiling to ARM64EC.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f