[Offload][Test] Add llvm bin in the PATH for offload-unit suite (#213149)

This PR makes the offload-unit suite put llvm bin directory on PATH so
that tests need lld can find. It fixes the issue exposed in:
https://github.com/llvm/llvm-project/pull/212860

offload/test/unit/lit.cfg.py

@@ -13,6 +13,17 @@ config.name = "Offload-Unit"
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = []
 
+# Add the tools bin dir to the search path so the JIT tests can
+# find it. Prefer the tools from the configured LLVM install or
+# bootstrapping build.
+if config.bin_llvm_tools_dir:
+    old_path = config.environment.get("PATH")
+    config.environment["PATH"] = (
+        f"{config.bin_llvm_tools_dir}{os.path.pathsep}{old_path}"
+        if old_path
+        else config.bin_llvm_tools_dir
+    )
+
 # test_source_root: The root path where tests are located.
 # test_exec_root: The root path where tests should be run.
 config.test_exec_root = config.unittest_dir

offload/test/unit/lit.site.cfg.in

@@ -3,6 +3,7 @@
 config.library_dir = "@LIBOMPTARGET_LIBRARY_DIR@"
 config.unittest_dir = "@OFFLOAD_UNITTEST_DIR@"
 config.llvm_build_mode = lit_config.substitute("@LLVM_BUILD_MODE@")
+config.bin_llvm_tools_dir = "@LLVM_TOOLS_BINARY_DIR@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@CMAKE_CURRENT_SOURCE_DIR@/unit/lit.cfg.py")