Avoid infinite recursion with identity variables.

Some generators like gypd and gypsh define the generator_default_variables
as an identity expansion. For example, the variable 'INTERMEDIATE_DIR'
would expand to '<(INTERMEDIATE_DIR)' which lends to an infinite recursion
if a .gyp file uses any of those variables.

This patch detects trivial infinite recursive variable expansions like
this one and leaves them that way.

Patch by Alejandro Deymonnaz <deymo@chromium.org>

TEST=`gyp --debug=variables --format=gypd test.gyp` shows avoiding
infinite recursion message when test.gyp has an INTERMEDIATE_DIR
variable expansion.

Review URL: https://codereview.chromium.org/417113009/

git-svn-id: http://gyp.googlecode.com/svn/trunk@1958 78cadc50-ecff-11dd-a971-7dbc132099af
1 file changed