base.bbclass: warn when there is trailing slash in S or B variables
* to make sure we won't hit such corner cases in future add a warning
to prevent trailing slashes and duplicated slashes even when they
in most cases don't cause harm
* only a few cases were found in layers included in my world builds:
oe-core: 1
meta-oe: 7
meta-python2: 1
meta-qt5: 1
meta-aws: 1
will send patches for these once this warning is approved for oe-core
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
