Disable building C++ tests for Linux

Due to the use of multiple build systems, link dependencies between C++
and Rust where C++ does the final linking will fail. Until we have full
Bazel build, we can't enable these tests again.

Bug: 190750167
Tag: #floss
Test: Build for Linux
Change-Id: Iadd7dafe9635f606c2289eb246e3e2eb4931e92c