[lld] [llvm] [DTLTO][LLD][ELF] Add support for Integrated Distributed ThinLTO (PR #142757)

[via llvm-commits]

================
@@ -36,6 +36,7 @@
 
 llvm_config.use_default_substitutions()
 llvm_config.use_lld()
+config.substitutions.append(("%llvm_src_root", config.llvm_src_root))
----------------
bd1976bris wrote:

The line in `lit.site.cfg.py.in` just sets the `lit` config variable `config.llvm_src_root`. This is also done in `LLD` 
: https://github.com/llvm/llvm-project/blob/d59e0ba80b85b5b74995ee441b681d51b2a5d1b0/lld/test/lit.site.cfg.py.in#L6. This line is just adding a substitution so that the value can be used in `lit` tests. The `Clang` tests add substitution based off this value here: https://github.com/llvm/llvm-project/blob/d59e0ba80b85b5b74995ee441b681d51b2a5d1b0/clang/test/utils/update_cc_test_checks/lit.local.cfg#L45.

https://github.com/llvm/llvm-project/pull/142757