These scripts are becoming more of nuisance, than a value-add;
particularly since we've been building releases using Guix. Adding new
(release bin) tests can be harder, because it requires constructing a
failing test, which is becoming less easy e.g trying to disable a
feature or protection that has been built into the compiler/toolchain by
default.
In the pre-Guix days, these were valuable to sanity-check the environment,
because we were pulling that pre-built from Ubuntu, with little control.
At this point, it's less clear what these scripts are (sanity) checking.
Note that these also weren't completely ported to CMake (#31698), see
also #31715 which contains other fixes that would be needed for these
test-tests, to accomodate future changes.
The use of `PACKAGE_NAME` for the project's variable name is
problematic, as this name is commonly used in CMake's interface
variables. If third-party CMake code handles with scopes improperly,
our `PACKAGE_NAME` variable could end up with an unexpected value.
This change avoids such conflicts by renaming all `PACKAGE_*` variables
to `CLIENT_*`.
