#62 Fix ARM64 support for Visual Studio 2017

[Pete Batard]

• Make sure stdint.h is always used with MSVC on ARM/ARM64, since all the versions of Visual Studio that support ARM or ARM64 have that header. Without this, uint64_t would be defined to unsigned long, which is 32-bits in the Microsoft world...
• Also fix aarch64/initplat.c so that memset/memcpy only apply to gcc. Otherwise MSVC throws an error for __SIZE_TYPE__

[Pete Batard]

Updating this patch to v2, since it turns out MSVC will also emit memset and memcpy intrinsics that we can use an implementation for. This is true for both ARM and ARM64.
To make this work, I'm defining __SIZE_TYPE__ to UINTN if not already defined.

[Nigel Croxon]

Patch V2 accepted.
commit id 39ce220cb6fde14bedf2ef61695f3d20726e41ef