base: add ability to provide further details when using LICENSE_FLAGS

Recipes with proprietary licenses often need to use LICENSE_FLAGS so
that the user can opt-in with consent. However, if you don't consent
then the error simply tells you the license identifier but not further
context.

Add a new variable LICENSE_FLAGS_DETAILS, which will be looked in for a
flag with the name of the licence.  If found then the contents are
printed as a source of further details.

For example, a recipe with an EULA may set:

  LICENSE_FLAGS = "FooBar-EULA"
  LICENSE_FLAGS_DETAILS[FooBar-EULA] = "https://example.com/eula"

If Foobar-EULA isn't in LICENSE_FLAGS_ACCEPTED then the error message is
more useful:

  Has a restricted license 'FooBar-EULA' which is not listed in your
  LICENSE_FLAGS_ACCEPTED. For further details, see
  https://example.com/eula.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions