runqueue: Ensure task environment is correct

This fixes two problems:

a) Variables which were in the parent environment but not set as "export"
   variables in the datastore could end up in the task environment

b) oe.environ.update() can't cope with the generator returned by
   bb.data.exported_vars()

Whilst the updated code isn't as neat, it does do the expected thing,
sets the environment correctly and stops unwanted values leaking into
the task environment.

(Bitbake rev: 67e5e23034c5ec2b9efcca935242830306c0048d)

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

bitbake/lib/bb/runqueue.py

@@ -1072,6 +1072,7 @@ class RunQueueExecute:
         # a fork() or exec*() activates PSEUDO...
 
         envbackup = {}
+        fakeenv = {}
         umask = None
 
         taskdep = self.rqdata.dataCache.task_deps[fn]
@@ -1087,6 +1088,7 @@ class RunQueueExecute:
             for key, value in (var.split('=') for var in envvars):
                 envbackup[key] = os.environ.get(key)
                 os.environ[key] = value
+                fakeenv[key] = value
 
             fakedirs = (self.rqdata.dataCache.fakerootdirs[fn] or "").split()
             for p in fakedirs:
@@ -1136,7 +1138,14 @@ class RunQueueExecute:
                 for h in self.rqdata.hash_deps:
                     the_data.setVar("BBHASHDEPS_%s" % h, self.rqdata.hash_deps[h])
 
-                os.environ.update(bb.data.exported_vars(the_data))
+                # exported_vars() returns a generator which *cannot* be passed to os.environ.update() 
+                # successfully. We also need to unset anything from the environment which shouldn't be there 
+                exports = bb.data.exported_vars(the_data)
+                bb.utils.empty_environment()
+                for e, v in exports:
+                    os.environ[e] = v
+                for e in fakeenv:
+                    os.environ[e] = fakeenv[e]
 
                 if quieterrors:
                     the_data.setVarFlag(taskname, "quieterrors", "1")