[libxslt] Use Python3 if compatible

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 9835e6f611aca6b0e1a2c15a30a19100742cf7b4
Author: Markus Rickert <rickert fortiss org>
Date:   Mon Feb 22 21:14:15 2021 +0100

    Use Python3 if compatible

 CMakeLists.txt | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)
---
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7d990784..4a88a44c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,6 +8,7 @@ include(CheckCSourceCompiles)
 include(CheckFunctionExists)
 include(CheckIncludeFiles)
 include(CheckLibraryExists)
+include(CheckSymbolExists)
 include(CMakePackageConfigHelpers)
 include(GNUInstallDirs)
 
@@ -49,8 +50,17 @@ if(LIBXSLT_WITH_CRYPTO)
 endif()
 
 if(LIBXSLT_WITH_PYTHON)
-       find_package(Python2 COMPONENTS Interpreter Development REQUIRED)
-       set(LIBXSLT_PYTHON_INSTALL_DIR ${Python2_SITEARCH} CACHE PATH "Python bindings install directory")
+       check_include_files(unistd.h HAVE_UNISTD_H)
+       check_symbol_exists(F_GETFL fcntl.h HAVE_F_GETFL)
+       if(HAVE_UNISTD_H AND HAVE_F_GETFL)
+               find_package(Python COMPONENTS Interpreter Development REQUIRED)
+       else()
+               find_package(Python2 COMPONENTS Interpreter Development REQUIRED)
+               add_library(Python::Python ALIAS Python2::Python)
+               set(Python_EXECUTABLE ${Python2_EXECUTABLE})
+               set(Python_SITEARCH ${Python2_SITEARCH})
+       endif()
+       set(LIBXSLT_PYTHON_INSTALL_DIR ${Python_SITEARCH} CACHE PATH "Python bindings install directory")
 endif()
 
 if(LIBXSLT_WITH_THREADS)
@@ -366,7 +376,7 @@ if(LIBXSLT_WITH_PYTHON)
        set(ENV{SRCDIR} ${CMAKE_CURRENT_SOURCE_DIR}/python)
        execute_process(
                COMMAND
-               ${Python2_EXECUTABLE}
+               ${Python_EXECUTABLE}
                ${CMAKE_CURRENT_SOURCE_DIR}/python/generator.py
                ${CMAKE_CURRENT_SOURCE_DIR}/doc/libxslt-api.xml
                ${CMAKE_CURRENT_SOURCE_DIR}/python/libxslt-python-api.xml
@@ -393,7 +403,7 @@ if(LIBXSLT_WITH_PYTHON)
                PUBLIC
                $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/python>
        )
-       target_link_libraries(LibXsltMod LibXslt LibExslt Python2::Python)
+       target_link_libraries(LibXsltMod LibXslt LibExslt Python::Python)
        set_target_properties(
                LibXsltMod
                PROPERTIES