qitoolchain: document cross toolchains and packages that set compile flags
qitoolchain: document cross toolchains and packages that set compile flags

Change-Id: I6bd9ed2f8b0ea550e48996975e802436c6c422d4
Reviewed-on: http://gerrit.aldebaran.lan/61579
Reviewed-by: jsuchard <65b43dbf56fcfd338b9cf3c99fe74c5632a9cf23@aldebaran.com>
Tested-by: gerrit
Reviewed-by: vbarbaresi <371b46c96c99af52f4f920034e4fcb63ece5bdb5@aldebaran-robotics.com>

aldebaran/qibuild,aldebaran/qibuild,aldebaran/qibuild,aldebaran/qibuild