fltk: Use the mesa-glu Conan package

[jwillikers]

This is done the same way as for the FreeGLUT package in #22428. Fixes #22944.

[jwillikers]

Since fltk is CMake-based, I'll likely need to upstream a fix for locating GLU.

[jcar87]

#23649

[jwillikers]

@jcar87 I don't know if you meant to close this one as it has to do with mesa-glu and not libglvnd. It's a pretty different library.

[jcar87]

Apologies! Didn't mean to close this one - this one needs a review in the similar vein, as the pattern is very similar - but indeed this is not the same case as the others

[jwillikers]

GLU is way simpler in terms of complexity.

[jwillikers]

Looks like a timeout error in CI.

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 10 (3d1e0ae9c1882d385e95deb342be7716ffb7ed87):

• fltk/1.3.9:
  All packages built successfully! (All logs)

• fltk/1.3.8:
  All packages built successfully! (All logs)

---

Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 10 (3d1e0ae9c1882d385e95deb342be7716ffb7ed87):

• fltk/1.3.8:
  All packages built successfully! (All logs)

• fltk/1.3.9:
  All packages built successfully! (All logs)

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions]

This pull request has been automatically closed because it has not had recent activity. Thank you for your contributions.