[lldb/CMake] Use PYTHON_HOME as a hint to find Python 3.

http://lists.llvm.org/pipermail/lldb-dev/2020-February/015998.html

Differential revision: https://reviews.llvm.org/D75275

lldb/cmake/modules/FindPythonInterpAndLibs.cmake

@@ -10,6 +10,8 @@ else()
   find_package(SWIG 2.0)
   if (SWIG_FOUND)
     if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
+      # Use PYTHON_HOME as a hint to find Python 3.
+      set(Python3_ROOT_DIR PYTHON_HOME)
       find_package(Python3 COMPONENTS Interpreter Development)
       if (Python3_FOUND AND Python3_Interpreter_FOUND)
         set(PYTHON_LIBRARIES ${Python3_LIBRARIES})