[lldb] make lit use the same Python executable for building and testing (llvm#143756)

When testing LLDB, we want to make sure to use the same Python as the
one we used to build it.

This patch uses the CMake variable `Python3_ROOT_DIR` to add the correct
Python to the `PATH` in LLDB lit tests, in order to ensure of this.

Please see swiftlang/swift#82063 for the
original issue.

This is a continuation of swiftlang/swift#82063.

Author: charles-zablit

lldb/cmake/modules/FindPythonAndSwig.cmake

@@ -6,7 +6,9 @@
 
 macro(FindPython3)
   # Use PYTHON_HOME as a hint to find Python 3.
-  set(Python3_ROOT_DIR "${PYTHON_HOME}")
+  if(NOT Python3_ROOT_DIR)
+    set(Python3_ROOT_DIR "${PYTHON_HOME}")
+  endif()
   find_package(Python3 COMPONENTS Interpreter Development)
   if(Python3_FOUND AND Python3_Interpreter_FOUND)
 

lldb/test/API/lit.cfg.py

@@ -367,3 +367,10 @@ def delete_module_cache(path):
 # Propagate XDG_CACHE_HOME
 if "XDG_CACHE_HOME" in os.environ:
     config.environment["XDG_CACHE_HOME"] = os.environ["XDG_CACHE_HOME"]
+
+# Some steps required to initialize the tests dynamically link with python.dll
+# and need to know the location of the Python libraries. This ensures that we
+# use the same version of Python that was used to build lldb to run our tests.
+config.environment["PATH"] = os.path.pathsep.join(
+    (config.python_root_dir, config.environment.get("PATH", ""))
+)

lldb/test/API/lit.site.cfg.py.in

@@ -20,6 +20,7 @@ config.llvm_use_sanitizer = "@LLVM_USE_SANITIZER@"
 config.target_triple = "@LLVM_TARGET_TRIPLE@"
 config.lldb_build_directory = "@LLDB_TEST_BUILD_DIRECTORY@"
 config.python_executable = "@Python3_EXECUTABLE@"
+config.python_root_dir = "@Python3_ROOT_DIR@"
 config.lua_executable = "@LUA_EXECUTABLE@"
 config.lldb_lua_cpath = "@LLDB_LUA_CPATH@"
 config.lua_test_entry = "TestLuaAPI.py"

lldb/test/Shell/lit.cfg.py

@@ -224,3 +224,6 @@ def calculate_arch_features(arch_string):
 # location of the Python libraries. This ensures that we use the same
 # version of Python that was used to build lldb to run our tests.
 config.environment["PYTHONHOME"] = config.python_root_dir
+config.environment["PATH"] = os.path.pathsep.join(
+    (config.python_root_dir, config.environment.get("PATH", ""))
+)