community/lldb: fix build with non-default clang
Due to the switch to LLVM 19 as the new default, add the non-default version to $PATH so it can be detected.
Rebuild error on the 3.21 loongarch64 builder:
CMake Error at /usr/share/cmake/Modules/CMakeDetermineCCompiler.cmake:49 (message):
Could not find compiler set in environment variable CC:
clang.
Call Stack (most recent call first):
CMakeLists.txt:19 (project)
CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
-- Configuring incomplete, errors occurred!