Add -verrors=num switch to control error limit
Add -verrors=0 for fail_compilation tests by default
Remove -verrors swithc from the help messages

Save the lines of help message so it's not very useful for the compiler users.
Merge pull request #4189 from 9rnsr/refactor_ctfe

[Refactoring] improve CTFE interpreter code
Merge pull request #4184 from 9rnsr/sw_verrors

Add a new compiler switch -verrors=num to control error report limit
Simplify CallExp::interpret() and support DotTypeExp in CTFE

Handle function values in each CTFE steps, then interpreting CallExp::e1 just only once will be enough.

Problematic case is a __cpctor call. In it, the 'this' expression is an
unilitialized variable so we need to initalize it before the interpretation of e1.

Also simplify ThisExp::interpret, comes from CallExp improvement.
Simplify CTFE interpreter

- Merely distinguish CTFE values and CTFE references.
- Improve any reference handling, including 'this' expresison.
Add CtfeResult