lib/oe/recipeutils: patch_recipe(): fix handling of values across includes/classes
If we were setting a variable and part of the variable's value was being
set in a class or a .inc file, we were still just setting the value
outright on the assumption that it was too hard to do otherwise. With
some careful use of the variable history we can do better for certain
situations i.e. when the recipe does not currently set the value
outright.
Additionally, correctly remove _appends for variables we are changing if
we're trying to remove the value added in the _append.
Fixes [YOCTO #12623] and partially fixes [YOCTO #9360].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
