This makes sure that BUILDING_V8_SHARED and USING_V8_SHARED are not
both set at once.

Change-Id: Iba3a4fac37518b6ec3658da4575453a7967ece0f
Bug: v8:8855
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1627978Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62369}