Export generator flavor to gyp scripts

pylib/gyp/__init__.py

Index: pylib/gyp/__init__.py
diff --git a/pylib/gyp/__init__.py b/pylib/gyp/__init__.py
index b10d97a93bd0d57c847b4b52d6857dc3ed0a1243..ac6d918b84992236ac638e27dc709db496498ce0 100755
--- a/pylib/gyp/__init__.py
+++ b/pylib/gyp/__init__.py
@@ -59,7 +59,6 @@ def Load(build_files, format, default_variables={},
   if params is None:
     params = {}
 
-  flavor = None
   if '-' in format:
     format, params['flavor'] = format.split('-', 1)
 
@@ -69,6 +68,7 @@ def Load(build_files, format, default_variables={},
   # named WITH_CAPITAL_LETTERS to provide a distinct "best practice" namespace,
   # avoiding collisions with user and automatic variables.
   default_variables['GENERATOR'] = format
+  default_variables['GENERATOR_FLAVOR'] = params.get('flavor', '')
 
   # Format can be a custom python file, or by default the name of a module
   # within gyp.generator.