feat: support UseCython by itself

Signed-off-by: Henry Schreiner <[email protected]>

Author: henryiii

src/cython_cmake/cmake/UseCython.cmake

@@ -76,7 +76,6 @@ if(CMAKE_VERSION VERSION_LESS "3.7")
   message(FATAL_ERROR "CMake 3.7 required for DEPFILE")
 endif()
 
-
 function(Cython_compile_pyx)
   cmake_parse_arguments(
     PARSE_ARGV 0
@@ -92,6 +91,16 @@ function(Cython_compile_pyx)
   endif()
   list(GET ALL_INPUT 0 INPUT)
 
+  if(DEFINED CYTHON_EXECUTABLE)
+    set(_cython_command "\"${CYTHON_EXECUTABLE}\"")
+  elseif(DEFINED Python_EXECUTABLE)
+    set(_cython_command "\"${Python_EXECUTABLE}\" -m cython")
+  elseif(DEFINED Python3_EXECUTABLE)
+    set(_cython_command "\"${Python3_EXECUTABLE}\" -m cython")
+  else()
+    message(FATAL_ERROR "Cython executable not found")
+  endif()
+
   # Set target language
   if(NOT CYTHON_LANGUAGE)
     get_property(_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
@@ -164,7 +173,7 @@ function(Cython_compile_pyx)
       "${CYTHON_OUTPUT}"
       "${depfile_path}"
     COMMAND
-      Cython::Cython
+      ${_cython_command}
       ${language_arg}
       ${CYTHON_CYTHON_ARGS}
       --depfile