Update to the new ninja-fied ab.

build/utils.py

@@ -11,6 +11,7 @@ from build.ab import (
 from os.path import relpath, splitext, join, basename, isfile
 from glob import iglob
 import fnmatch
+import subprocess
 
 
 def filenamesmatchingof(xs, pattern):
@@ -51,6 +52,11 @@ def itemsof(pattern, root=None, cwd=None):
     return result
 
 
+def shell(args):
+    r = subprocess.check_output(args)
+    return r.decode("utf-8").strip()
+
+
 @Rule
 def objectify(self, name, src: Target, symbol):
     simplerule(