[lldb] Remove Python 2 fallback and make Python 3 the only supported configuration.

[JDevlieghere]

Summary

This removes the fallback to Python 2 and makes Python 3 the only supported configuration.

This is the first step as proposed on the mailing list (http://lists.llvm.org/pipermail/lldb-dev/2020-August/016387.html) to fully migrate to Python 3 over the coming releases.

[mgorny]

I wonder if we can remove the helper variables such as PYTHON_LIBRARIES now.

[JDevlieghere]

In D85942#2217494, @mgorny wrote:

I wonder if we can remove the helper variables such as PYTHON_LIBRARIES now.

Yep, that was going to be the next patch :-)

lldb/cmake/modules/FindPythonInterpAndLibs.cmake

mark_as_advanced(
       PYTHON_LIBRARIES
       PYTHON_INCLUDE_DIRS
       PYTHON_EXECUTABLE
       PYTHON_RPATH
       SWIG_EXECUTABLE)
   endif()
 endmacro()
 
-macro(FindPython2)
-  # Use PYTHON_HOME as a hint to find Python 2.
-  set(Python2_ROOT_DIR "${PYTHON_HOME}")
-  find_package(Python2 COMPONENTS Interpreter Development)
-  if(Python2_FOUND AND Python2_Interpreter_FOUND)
-    set(PYTHON_LIBRARIES ${Python2_LIBRARIES})
-    set(PYTHON_INCLUDE_DIRS ${Python2_INCLUDE_DIRS})
-    set(PYTHON_EXECUTABLE ${Python2_EXECUTABLE})
-
-    set(PYTHON2_FOUND TRUE)
-    mark_as_advanced(
-      PYTHON_LIBRARIES
-      PYTHON_INCLUDE_DIRS
-      PYTHON_EXECUTABLE
-      SWIG_EXECUTABLE)
-  endif()
-endmacro()
-
 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 (LLDB_PYTHON_VERSION)
-      if (LLDB_PYTHON_VERSION VERSION_EQUAL "2")
-        FindPython2()
-      elseif(LLDB_PYTHON_VERSION VERSION_EQUAL "3")
-        FindPython3()
-      endif()
-    else()
-      FindPython3()
-      if (NOT PYTHON3_FOUND AND NOT CMAKE_SYSTEM_NAME STREQUAL Windows)
-        FindPython2()
-      endif()
-    endif()
   else()
     message(STATUS "SWIG 2 or later is required for Python support in LLDB but could not be found")
   endif()
 
   include(FindPackageHandleStandardArgs)
   find_package_handle_standard_args(PythonInterpAndLibs
                                     FOUND_VAR
                                       PYTHONINTERPANDLIBS_FOUND
                                     REQUIRED_VARS
                                       PYTHON_LIBRARIES
                                       PYTHON_INCLUDE_DIRS
                                       PYTHON_EXECUTABLE
                                       SWIG_EXECUTABLE)
 endif()