[llvm] [unittest] Allow LLVM unit test to run under a wrapper program. (PR #66821)

[via llvm-commits]

================
@@ -7,6 +7,7 @@ config.llvm_obj_root = path(r"@LLVM_BINARY_DIR@")
 config.llvm_tools_dir = lit_config.substitute(path(r"@LLVM_TOOLS_DIR@"))
 config.llvm_build_mode = lit_config.substitute("@LLVM_BUILD_MODE@")
 config.shlibdir = lit_config.substitute(path(r"@SHLIBDIR@"))
+config.gtest_run_under = lit_config.substitute(r"@LLVM_GTEST_RUN_UNDER@")
----------------
zeroomega wrote:

> Can you set this variable in `llvm/CMakeLists.txt" as a cached value, defaulting to an empty string and providing a short description?

Done in https://github.com/llvm/llvm-project/pull/66821/commits/44b8052a0a64c550f885adf0db51bc3cde1f2c00

https://github.com/llvm/llvm-project/pull/66821