Disable Werror by default

We don't want everybody to have to go and tweak ~/.gyp/include.gypi
just for that purpose.

Change-Id: I67533a62246dea45c4b5a5a454f43d01328d472f
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>