Update BUILDCONFIG.gn to support Visual Studio 2017 Enterprise

Bug: skia:
Change-Id: I7723a545d2f5ed78f6637aa9b8990e28785f86fb
Reviewed-on: https://skia-review.googlesource.com/c/182191
Auto-Submit: Dawson Coleman <dawsonmcoleman@gmail.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed