Reland "Consider winsdk_samples a system library."

This reverts commit 231200f9483de38da96fb7bf16cab8e4f92d31f5.

Reason for revert: Using -imsvc instead of -isystem.

Change-Id: Iee2a616d846910dc56923bc8401076cd40bf69b3
TBR=phoglund@webrtc.org
Reviewed-on: https://webrtc-review.googlesource.com/76521
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>