lxc: Use gcc instead of clang compiler

[Deepak-Rathore580]

While compiling lxc with clang, it fails with compilation error and not compatible with clang compiler. Hence, updated TOOLCHAIN of lxc to use gcc.

---

Contributor checklist

• Changes have been tested
• Signed-off-by is present
• The PR complies with the Open Embedded Commit Patch Message Guidelines

Reviewer Guidelines

• When submitting a review, please pick:
  • 'Approve' if this change would be acceptable in the codebase (even if there are minor or cosmetic tweaks that could be improved).
  • 'Request Changes' if this change would not be acceptable in our codebase (e.g. bugs, changes that will make development harder in future, security/performance issues, etc).
  • 'Comment' if you don't feel you have enough information to decide either way (e.g. if you have major questions, or you don't understand the context of the change sufficiently to fully review yourself, but want to make a comment)

[kraj]

we do not enable thin-lto by default, but its a possible DISTRO_FEATURE so it might be better to check for this in DISTRO_FEATURES and then resort to always using gcc toolchain