The current handling had a fairly bad issue: multiple calls to
`set_tests_properties` to set envvars of a same test.
This does not work, only the last call is effective, all previous
ones have absolutely no effect.
This has been addressed by moving all 'set envvar for test' logic into a
single CMake function, `blender_test_set_envvars`.
This function takes optional extra envvars if needed, and define a set
of default ones (currently, `PATH` from `PLATFORM_ENV_INSTALL` if
defined, and the 'nuke' `exitcode=0` `LSAN_OPTIONS` if relevant).
NOTE: The way `blender_test_set_envvars` handles extra envvars passed to
it as parameter is fairly basic and unsafe, in that there is no check
whether a same envvar is defined more than once. Think for now this is
an acceptable limitation.
NOTE: Although this commit _should_ be a non-functional change one, the
unification of the handling of all envvars makes it hard to ensure there is no
side effects.
The `PATH` envvar e.g. was set to either `PLATFORM_ENV_INSTALL` if defined,
or a copy of that variable's definition, but only in Windows case. So technically,
the behavior for this envvar is changed.
3e744db9fe