ninja: simplify configure step

component/ninja/buildout.cfg

 [buildout]
-extends =
-  ../defaults.cfg
 parts =
   ninja
 
@@ -10,7 +8,7 @@ shared = true
 version = 1.10.2
 url = https://github.com/ninja-build/ninja/archive/refs/tags/v${:version}.tar.gz
 md5sum = 639f75bc2e3b19ab893eaf2c810d4eb4
-configure-command = ${python:executable} configure.py
+configure-command = ${buildout:executable} configure.py
 configure-options = --bootstrap --verbose
 make-binary = true
 post-install =