framework: make llvm.mk aware of base compilers version not add dependency unnecessarily

[tcberner]

Summary

Heavily WIP.

Idea is to not add a dependency on devel/llvm* when base's clang is newer than the version llvm.mk calculated.

• behaviour only affects :build and :run, not :lib.
• behaviour can be turned off by :force.

Test Plan

Actually test :D

[adamw]

This is a really good idea. The current llvm.mk causes some POLA problems for people who don't have DEFAULT_VERSIONS=llvm=... set, where suddenly llvm90 is being used to build things.

[tcberner]

• framework: rough conversion of the tree to llvm.mk

[adamw]

devel/lua-language-server/Makefile

40 ↗

(On Diff #114688)

Is this really correct? How is USES=llvm to know that it needs llvm13? I am not totally understanding what USES=llvm is doing, but it seems like this points CPP/CC/CXX to binaries that the framework isn't ensuring are installed.

[tcberner]

• framework: cleanup of conversion 1/n

[tcberner]

• framework: cleanup of conversion 2/n (define LLVM_C* vars)

[jbeich]

emulators/wine-proton/Makefile

2 ↗

(On Diff #114690)

Looks unrelated and would break build due to distinfo desync.

graphics/blender/Makefile

2 ↗

(On Diff #114690)

Looks unrelated and would break build due to distinfo desync.

graphics/mesa-devel/Makefile

3 ↗

(On Diff #114690)

Looks unrelated and would break build due to distinfo desync.

net-im/telegram-desktop/Makefile

2 ↗

(On Diff #114690)

Looks unrelated and would break build due to distinfo desync.

[tcberner]

Only export variables for now.

[tcberner]

fix typo in CPP

[bofh]

I just ran a smaller exp-run with the specific ports of interest and