Refactor: get rid of builtin.*

[YerinAlexey]

Problem

First of, using builtin makes generators dependent on C-style languages, which is a problem for bare-metal (x86, AVR, *Assembly etc). And even for C or Node this faces the problem of wrong error reporting as builtin is not cut off.

Possible solutions

• We can make builtin optional so binary targets wouldn't need it if they don't want to (right now it's a requirement). This will not fix (2) though
• Get rid of builtin all together and generate special functions like printf or exit on the fly