[LyX/master] Cmake build: Consider for cmake versions <= 3.12 while searching for python

[Kornel Benko]

commit 5e436ce9e5c8b1bf6a06d27b9771c7b7e8ca6be0
Author: Kornel Benko <kornel at lyx.org>
Date:   Thu Nov 28 21:51:47 2019 +0100

    Cmake build: Consider for cmake versions <= 3.12 while searching for python
    
    This partially reverts d17dfe6f
---
 CMakeLists.txt |   27 +++++++++++++++++++--------
 1 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 52290e8..12b81a6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -792,16 +792,27 @@ unset(LYX_PYTHON_EXECUTABLE CACHE)
 unset(PYTHON_VERSION_MAJOR)
 unset(PYTHON_VERSION_MINOR)
 unset(PYTHON_VERSION_STRING)
-find_package(Python3 3.5 QUIET)
-if(NOT Python3_Interpreter_FOUND)
-  unset(PYTHON_EXECUTABLE CACHE)
-  find_package(Python2 2.0 REQUIRED)
-  if(NOT PYTHON_VERSION_STRING VERSION_LESS 2.8)
-    message(FATAL_ERROR "Python interpreter found, but is not suitable")
+if (CMAKE_VERSION VERSION_LESS "3.13")
+  find_package(PythonInterp 3.5 QUIET)
+  if(NOT PYTHONINTERP_FOUND)
+    find_package(PythonInterp 2.0 REQUIRED)
+    if(NOT PYTHON_VERSION_STRING VERSION_LESS 2.8)
+      message(FATAL_ERROR "Python interpreter found, but is not suitable")
+    endif()
   endif()
-  set(LYX_PYTHON_EXECUTABLE ${Python2_EXECUTABLE} CACHE FILEPATH "Python to be used by LyX")
+  set(LYX_PYTHON_EXECUTABLE ${PYTHON_EXECUTABLE} CACHE FILEPATH "Python to be used by LyX")
 else()
-  set(LYX_PYTHON_EXECUTABLE ${Python3_EXECUTABLE} CACHE FILEPATH "Python to be used by LyX")
+  find_package(Python3 3.5 QUIET)
+  if(NOT Python3_Interpreter_FOUND)
+    unset(PYTHON_EXECUTABLE CACHE)
+    find_package(Python2 2.0 REQUIRED)
+    if(NOT PYTHON_VERSION_STRING VERSION_LESS 2.8)
+      message(FATAL_ERROR "Python interpreter found, but is not suitable")
+    endif()
+    set(LYX_PYTHON_EXECUTABLE ${Python2_EXECUTABLE} CACHE FILEPATH "Python to be used by LyX")
+  else()
+    set(LYX_PYTHON_EXECUTABLE ${Python3_EXECUTABLE} CACHE FILEPATH "Python to be used by LyX")
+  endif()
 endif()
 
 if(LYX_NLS)