Specify buildable target for goma latest client clexe builder

To fix following builders:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win%20cl.exe%20Goma%20Latest%20Client%20LocalOutputCache
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/WinMSVC64%20Goma%20Latest%20Client

Change-Id: Ic6acb7b8a123165dcda0fc98d3c07c55bd7de38a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1498746
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637876}
2 files changed