bitbake/gcc: Enable a shared common source tree

This patch is a quick proof of concept to show how source code could
be shared between recipes which use ${B} to have a separate build
directory compared to source directory ${S}.

Issues:

a) gcc uses sed and creates config files against ${S} which means
the directory should not be shared. Need to change the way that works.

b) Could be extended to cover eglibc except there is a patch applied
against nativesdk versions which again makes the source incompatible.

c) Need to clean up the layout in work-shared and make a directory level deeper
to ensure patch separation.

d) clean task does not remove stamps

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cache.py

@@ -55,6 +55,7 @@ recipe_fields = (
     'provides',
     'task_deps',
     'stamp',
+    'stamp_base',
     'stamp_extrainfo',
     'broken',
     'not_world',
@@ -160,6 +161,7 @@ class RecipeInfo(namedtuple('RecipeInfo', recipe_fields)):
             broken           = cls.getvar('BROKEN', metadata),
             not_world        = cls.getvar('EXCLUDE_FROM_WORLD', metadata),
             stamp            = cls.getvar('STAMP', metadata),
+            stamp_base       = cls.flaglist('stamp-base', tasks, metadata),
             stamp_extrainfo  = cls.flaglist('stamp-extra-info', tasks, metadata),
             packages_dynamic = cls.listvar('PACKAGES_DYNAMIC', metadata),
             depends          = cls.depvar('DEPENDS', metadata),
@@ -579,6 +581,7 @@ class CacheData(object):
         self.task_queues = {}
         self.task_deps = {}
         self.stamp = {}
+        self.stamp_base = {}
         self.stamp_extrainfo = {}
         self.preferred = {}
         self.tasks = {}
@@ -604,6 +607,7 @@ class CacheData(object):
         self.pkg_pepvpr[fn] = (info.pe, info.pv, info.pr)
         self.pkg_dp[fn] = info.defaultpref
         self.stamp[fn] = info.stamp
+        self.stamp_base[fn] = info.stamp_base
         self.stamp_extrainfo[fn] = info.stamp_extrainfo
 
         provides = [info.pn]