[lldb] Fix deps loading for lldb-python on Windows and Python3.8+ (in review swiftlang#9370)

Author: weliveindetail

lldb/bindings/python/CMakeLists.txt

@@ -196,6 +196,26 @@ function(finish_swig_python swig_target lldb_python_bindings_dir lldb_python_tar
       COMMENT "Copying Python DLL to LLDB binaries directory.")
   endif()
 
+  # Since Python3.8 the Windows runtime loads dependent DLLs only from the directory of the binary
+  # itself (and not Path). Windows has no notion RPATHs, so we must copy all DLLs that we depend on
+  # into the Python package. Plus swiftCore which is a transitive (but no direct) dependency.
+  if (WIN32 AND LLDB_ENABLE_SWIFT_SUPPORT)
+    # TARGET_RUNTIME_DLLS is supported in CMake 3.21+
+    if ("${CMAKE_VERSION}" VERSION_LESS "3.21.0")
+      if (LLDB_INCLUDE_TESTS)
+        message(SEND_ERROR
+          "Your CMake version is ${CMAKE_VERSION}. In order to run LLDB tests "
+          "on Windows please upgrade to 3.21.0 at least (or disable tests with "
+          "LLDB_INCLUDE_TESTS=Off)")
+      endif()
+    else()
+      # swiftCore is defined in swift/stdlib/public/core/CMakeLists.txt
+      # It's not configured yet, so we cannot depend on it.
+      add_custom_command(TARGET ${swig_target} POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy -t ${lldb_python_target_dir} $<TARGET_RUNTIME_DLLS:liblldb> ${SWIFT_BINARY_DIR}/bin/swiftCore.dll
+        COMMAND_EXPAND_LISTS)
+    endif()
+  endif()
 
 endfunction()