autotools.bbclass: Add functionality to force a clean of ${B} when reconfiguring...

autotools.bbclass: Add functionality to force a clean of ${B} when reconfiguring (and ${S} != ${B})

Unfortunately whilst rerunning configure and make against a project will mostly
work there are situations where it does not correctly do the right thing.

In particular, eglibc and gcc will fail out with errors where settings
do not match a previously built configuration. It could be argued they are
broken but the situation is what it is. There is the possibility of more subtle
errors too.

This patch adds removal of the build directory (${B}) when configure is
rerunning, the sstate checksum for do_configure has changed and ${S} != ${B}.
We could simply use a stamp but saving out the previous configuration checksum
adds some data at no real overhead.

If we find there are things where we want to disable this behaviour with
CONFIGURESTAMPFILE = "" in the recipe, or users could disable it globally.

[YOCTO #2774]
[YOCTO #2848]

This is particularly helpful for eglibc and gcc which use split builds by default and
are a particular source of reconfigure type problems.

(From OE-Core rev: f15f61af77cc4e52a037f509f8e49e1ea530cf35)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>