Currently this takes a return value, and in the error case sets it,
then has a separate if to hanle that. Instead just set the return
value in the error handler.
We'll need this in the llvm-config logic to determine the right
llvm-config to call on Fedora 30+, but this feels like the sort of
information that might be useful elsewhere. This does not expose this
information as part of the public API, it's only accessible at the
python layer.
1. They (and the others) all use PerMachineDefaultable. It's not the
best class, but consistency come first. (It and all of them can be
improved accross the board later.)
2. They use `None` as the default argument so as not to mutate what's
effectively a global variables. (Thanks @dcbaker!)
3. They have a `fallback` field to centralize authority on when
environment variables should be consulted.
First of all, I'd like compilers and other modules that environment.py
currently imports to be able to take these without creating
hard-to-follow module cycles.
Second of all, environment.py's exact purpose seems a bit obscured.
Splitting the data types (and basic pure functions) from the more
complex logic that infers that data seems like a good way to separate
concerns.
Dylan Baker