base: Fix license checksum rebuild problems
"MACHINE=qemux86-64 bitbake init-ifupdown; MACHINE=genericx86-64 bitbake init-ifupdown"
shows a rebuild when it would be expected. The reason is a LIC_FILES_CHKSUM which
contains file://${WORKDIR}, an absolute path which doesn't exist in the first build
but does in the second, causing a signature change and a rebuild.
Fix the problem by ignoring any file:// url which resolves since TMPDIR for
license file dependency purposes.
(From OE-Core rev:
f27ddf0de23871fc72cfc31f514f0e144aaa2082)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
