Windows doesn't support 'make', but CMake can build the generated files
using 'cmake --build'.

Also set host=x64 to ensure the 64-bit toolchain gets used, to avoid
LLVM linking issues.

Also define __i386__ and __x86_64__ macros.

Bug b/115344057

Change-Id: Idc3f78560b50e67b81a2e7a2490e0e5f23e6cc9d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27809Tested-by: Nicolas Capens <nicolascapens@google.com>
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>