Clarify warning for GYP variable merging.

build/gyp_helper.py

Index: build/gyp_helper.py
diff --git a/build/gyp_helper.py b/build/gyp_helper.py
index a2cc7e19cbc3578ba863e9ea214af78dafd48846..9be2b9e01519233207ace24cae0176376a00abb3 100644
--- a/build/gyp_helper.py
+++ b/build/gyp_helper.py
@@ -44,11 +44,17 @@ def apply_gyp_environment_from_file(file_path):
       if var in os.environ:
         behavior = 'replaces'
         if var == 'GYP_DEFINES':
-          os.environ[var] = file_val + ' ' + os.environ[var]
-          behavior = 'overrides'
+          result = file_val + ' ' + os.environ[var]
+          behavior = 'merges with, and individual components override,'
+        else:
+          result = os.environ[var]
         print 'INFO: Environment value for "%s" %s value in %s' % (
             var, behavior, os.path.abspath(file_path)
         )
+        string_padding = max(len(var), len(file_path), len('result'))
+        print '      %s: %s' % (var.rjust(string_padding), os.environ[var])
+        print '      %s: %s' % (file_path.rjust(string_padding), file_val)
+        os.environ[var] = result
       else:
         os.environ[var] = file_val