[clang] [lldb] Use CLANG_RESOURCE_DIR more consistently (PR #103388)

[Tulio Magno Quites Machado Filho via cfe-commits]

tuliom wrote:

> Is there an out-of-tree scenario where CLANG_RESOURCE_DIR needs to be replaced with something else at runtime, i.e. a real use-case for the optional CustomResourceDir optional argument I removed?

@kimgr I have also looked for this and I haven't found an use-case where this would be appropriate. In fact, I think it's wrong to not take `CLANG_RESOURCE_DIR` as part of the output from `driver::Driver::GetResourcesPath()` because that would generate wrong results for builds that do set `CLANG_RESOURCE_DIR`, e.g. Fedora's builds.

https://github.com/llvm/llvm-project/pull/103388