libraw: fix inconsistencies with upstream project

[valgur]

Summary

Changes to recipe: libraw/[*]

Motivation

The recipe uses a custom CMakelists.txt, which does not completely reproduce the logic in the project build scripts:

• The project builds two separate libraries - raw and raw_r. The only difference for the latter is that it's built with -pthread. I added it as an optional component to the recipe to avoid linking against both by accident in consuming recipes.
• The .pc files installed by the project include a -Iinclude/libraw compile flag not set by the recipe.
• The library provides a pure-C interface, but it requires linking against the C++ stdlib in that case.

The missing include dir path caused a compilation failure in imlib2.

Details

---

• Read the contributing guidelines
• Checked that this PR is not a duplicate: list of PRs by recipe
• Tested locally with at least one configuration using a recent version of Conan

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 1 (6bee75cf50ff1bf8d3cfe3a778f247f5d4e896b8):

• libraw/0.21.2:
  All packages built successfully! (All logs)

• libraw/0.20.2:
  All packages built successfully! (All logs)

• libraw/0.21.1:
  All packages built successfully! (All logs)

• libraw/0.20.0:
  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 1 (6bee75cf50ff1bf8d3cfe3a778f247f5d4e896b8):

• libraw/0.21.1:
  All packages built successfully! (All logs)

• libraw/0.20.2:
  All packages built successfully! (All logs)

• libraw/0.21.2:
  All packages built successfully! (All logs)

• libraw/0.20.0:
  All packages built successfully! (All logs)

[AbrilRBS]

Thanks a lot for taking the time to fix the recipe usage, and the detailed PR description, we appreciate it :)

The changes look good to me

[perseoGI]

LGTM