Fix build for LLVM 10.0.0rc1 extras

[williams_ct1.xyz]

Summary

EXTRAS are currently disabled due to configure errors, resulting in the missing EXTRAS option, and inability to build clang-tools-extra e.g. clang-tidy, clang-rename, clang-doc etc.
Missing lua dependency if LLDB option specified.

The issue was a patch from llvm90 that incorrectly patched CMakeLists.txt in llvm10

Test Plan

make stage (OK)
make stage-qa (Added USES+=lua for LLDB OPTION)
make package (OK)
make install (OK)
make deinstall (OK)

[brooks]

Thanks for the submission, I'll commit shortly (with a small tweak to the lua bits).