Find mutated variables and variables captured by closure.
Analyze lambdas if they are suitable for lambda lifting.
- FORM is a piece of Elisp code after macroexpansion.
- ENV is an alist mapping each enclosing lexical variable to its info.
I.e. each element has the form (VAR . (READ MUTATED CAPTURED CALLED)).
This function does not return anything but instead fills the
`cconv-captured+mutated' and `cconv-lambda-candidates' variables
and updates the data stored in ENV. (fn FORM ENV)