Add remill and gap portfiles

[xlauko]

Add remill and gap ports.

remill port allows to specify features cxx-common-llvm-14 or system-llvm to build with local install llvm or uses cxx-common provided LLVM.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
4 out of 5 committers have signed the CLA.

:white_check_mark: ekilmer
:white_check_mark: xlauko
:white_check_mark: Ninja3047
:white_check_mark: PappasBrent
:x: lkorenc
_{You have signed the CLA already but the status is still pending? Let us recheck it.}