[buck] always merge tenvs regardless of mode
[buck] always merge tenvs regardless of mode

Summary:
We cannot necessarily know if the previous capture phase was java or
clang, hence to be on the safe side we should always merge the global
tenvs when merging Buck targets.

Reviewed By: ngorogiannis

Differential Revision: D19175685

fbshipit-source-id: 8e7492e14

facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer