meson tests sharing a binary (and deviating in their env/args) will
produce temporary logs to the same directory, which is assumed to exist
only for the duration of a single test. This is problematic when running
tests in parallel, as one test may remove the directory before the
other(s) finish, causing a test flake.
This appends the each test's pid to the output directory to enforce
uniqueness and avoid the race.
Signed-off-by: Ryan Neph <ryanneph@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20779>
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