I don't think there are any tests for this but I did some command-line
tests and, at least for the things I tested, this preserves the code
behavior while avoiding backtracking issues in the regular expression.

Closes: #135

Python 3.9 on IBM i now properly returns "os400" for sys.platform
instead of claiming to be AIX as it did previously. While the IBM i PASE
environment is compatible with AIX, it is a subset and has numerous
differences which makes it beneficial to distinguish, however this means
that it now needs explicit support here.

They are probably not paths, and V8 uses an argument like that, so the
fix is needed in Node.js

Refs: nodejs/node#42115