Using a custom logging.yml we can instruct BitBake's logger to write all
warnings and errors into a separate log file.
Then after the build has finished we can see if the log file is empty and if
not show it and abort the build.
Change-Id: Ida835b5c822941fb513dfb1758b4ec195e0050fc
Signed-off-by: Ross Burton <ross.burton@arm.com>
35adaace0e