Fail to build for Windows Desktop ARM and ARM64

[WenceyWang]

Windows Desktop ARM and ARM64 failed to build for _mm_mfence() not aviliable.

bx/include/bx/inline/cpu.inl

Line 97 in be10327

_mm_mfence();

calls _mm_mfence(); which only work on x86 and

bx/include/bx/inline/cpu.inl

Line 11 in be10327

# if BX_PLATFORM_WINRT

only include MemoryBarrier() for WinRT.

We should let Windows build call MemoryBarrier() instead assume we have x86.

[bkaradzic]

Try:

	inline void memoryBarrier()
	{
#if BX_COMPILER_MSVC
#   if BX_CPU_ARM
		MemoryBarrier();
#   else
		_mm_mfence();
#   endif // BX_CPU_ARM
#else
		__sync_synchronize();
#endif // BX_COMPILER
	}

[WenceyWang]

I think we should use (!BX_CPU_X86) for this scenario.