speed up libplist-flutter

Formula/libplist-flutter.rb

diff --git a/Formula/libplist-flutter.rb b/Formula/libplist-flutter.rb
index 3e8c596..e49c721 100644
--- a/Formula/libplist-flutter.rb
+++ b/Formula/libplist-flutter.rb
@@ -22,8 +22,11 @@
       --prefix=#{prefix}
       --without-cython
     ]
-
-    system "./autogen.sh" if build.head?
+    
+    if build.head?
+      ENV["NOCONFIGURE"] = "TRUE"
+      system "./autogen.sh"
+    end
     system "./configure", *args
     system "make", "install", "PYTHON_LDFLAGS=-undefined dynamic_lookup"
   end