[libcxx] Use LIBCXX_EXECUTOR in new test configs

This allows cross-testing (by setting LIBCXX_EXECUTOR to point
to ssh.py) without making an entirely new test config file.

Implicitly, this also fixes quoting of the python executable name
(which is quoted in test/CMakeLists.txt).

Differential Revision: https://reviews.llvm.org/D115398

GitOrigin-RevId: c1a14a5c3e6fef181f920b66ec159b6bfac4d457
3 files changed