Fix setting Python3_ROOT_DIR on Windows

[isuruf]

Summary

Previously the value of Python3_ROOT_DIR was set to the string
"PYTHON_HOME" instead of the value of the variable named
PYTHON_HOME. This commit fixes that as CMake expects
a path as the value of Python3_ROOT_DIR

[JDevlieghere]

Can you explain why this is necessary?

[isuruf]

The intention of the code is to set the variable Python3_ROOT_DIR to the value of the variable PYTHON_HOME, but it was using just the string "PYTHON_HOME" instead.

[teemperor]

LGTM, PYTHON_HOME is apparently the Windows way we allow people to specify the python root when finding the package.

Please update the review description though with why this change was done that this isn't just documented in the comments here.

[teemperor]

@isuruf Do you have commit access or do you need this committed?

lldb/cmake/modules/FindPythonInterpAndLibs.cmake

 #.rst:
 # FindPythonInterpAndLibs
 # -----------
 #
 # Find the python interpreter and libraries as a whole.
 
 if(PYTHON_LIBRARIES AND PYTHON_INCLUDE_DIRS AND PYTHON_EXECUTABLE AND SWIG_EXECUTABLE)
   set(PYTHONINTERPANDLIBS_FOUND TRUE)
 else()
   find_package(SWIG 2.0)
   if (SWIG_FOUND)
     if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
       # Use PYTHON_HOME as a hint to find Python 3.
-      set(Python3_ROOT_DIR PYTHON_HOME)
+      set(Python3_ROOT_DIR "${PYTHON_HOME}")
       find_package(Python3 COMPONENTS Interpreter Development)
       if (Python3_FOUND AND Python3_Interpreter_FOUND)
         set(PYTHON_LIBRARIES ${Python3_LIBRARIES})
         set(PYTHON_INCLUDE_DIRS ${Python3_INCLUDE_DIRS})
         set(PYTHON_EXECUTABLE ${Python3_EXECUTABLE})
         mark_as_advanced(
           PYTHON_LIBRARIES
           PYTHON_INCLUDE_DIRS