ARROW-2049: [Python] Try searching for the Cython executable according to sysconfig

cpp/cmake_modules/FindCython.cmake

@@ -1,30 +0,0 @@
-# Find the Cython compiler.
-#
-# This code sets the following variables:
-#
-#  CYTHON_EXECUTABLE
-#
-# See also UseCython.cmake
-
-#=============================================================================
-# Copyright 2011 Kitware, Inc.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-#=============================================================================
-
-find_program( CYTHON_EXECUTABLE NAMES cython cython.bat )
-
-include( FindPackageHandleStandardArgs )
-FIND_PACKAGE_HANDLE_STANDARD_ARGS( Cython REQUIRED_VARS CYTHON_EXECUTABLE )
-
-mark_as_advanced( CYTHON_EXECUTABLE )

cpp/cmake_modules/UseCython.cmake

@@ -66,7 +66,6 @@ set( CYTHON_FLAGS "" CACHE STRING
   "Extra flags to the cython compiler." )
 mark_as_advanced( CYTHON_ANNOTATE CYTHON_NO_DOCSTRINGS CYTHON_FLAGS)
 
-find_package( Cython REQUIRED )
 find_package( PythonLibsNew REQUIRED )
 
 set( CYTHON_CXX_EXTENSION "cxx" )
@@ -132,7 +131,7 @@ function( compile_pyx _name pyx_target_name generated_files pyx_file)
 
   # Add the command to run the compiler.
   add_custom_target(${pyx_target_name}
-    COMMAND ${CYTHON_EXECUTABLE} ${cxx_arg} ${include_directory_arg}
+    COMMAND ${PYTHON_EXECUTABLE} -m cython ${cxx_arg} ${include_directory_arg}
     ${annotate_arg} ${no_docstrings_arg} ${cython_debug_arg}
     ${CYTHON_FLAGS}
     --output-file "${_name}.${extension}" ${pyx_location}