Improve install method of py port.

Author: viferga

source/ports/py_port/CMakeLists.txt

@@ -26,7 +26,7 @@ if(NOT OPTION_BUILD_GUIX)
 		set(PIP_BACKWARD_COMPATIBILITY "${CMAKE_COMMAND} -E env SETUPTOOLS_USE_DISTUTILS=stdlib")
 	endif()
 
-	install(CODE "execute_process(COMMAND ${PIP_BACKWARD_COMPATIBILITY} pip3 install ${PIP_BREAK_SYSTEM_PACKAGES} ${CMAKE_CURRENT_SOURCE_DIR})")
+	install(CODE "execute_process(COMMAND ${PIP_BACKWARD_COMPATIBILITY} ${Python3_EXECUTABLE} -m pip install ${PIP_BREAK_SYSTEM_PACKAGES} ${CMAKE_CURRENT_SOURCE_DIR})")
 endif()
 
 # Check if loaders are enabled