bitbake: codeparser: Allow code visitor expressions to be declared in metadata

Allow the metadata to define code visitor expressions which mean that
custom dependencies can be handled in function libraries.

An example is the qa.handle_error function in OE which can set something
like:

"""
def handle_error_visitorcode(name, args):
    execs = set()
    contains = {}
    warn = None
    if isinstance(args[0], ast.Constant) and isinstance(args[0].value, str):
        for i in ["ERROR_QA", "WARN_QA"]:
            if i not in contains:
                contains[i] = set()
        contains[i].add(args[0].value)
    else:
        warn = args[0]
        execs.add(name)
    return contains, execs, warn

handle_error.visitorcode = handle_error_visitorcode
"""

Meaning that it can have contains optimisations on ERROR and WARN_QA
instead of hard dependencies.

One drawback to this solution is the parsing order. Functions with
visitorcode need to be defined before anything else references them
or the visitor code will not function for the earlier references.

(Bitbake rev: 5bd0c65c217394cde4c8e382eba6cf7f4b909c97)

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

bitbake/lib/bb/cache.py

@@ -28,7 +28,7 @@ import shutil
 
 logger = logging.getLogger("BitBake.Cache")
 
-__cache_version__ = "155"
+__cache_version__ = "156"
 
 def getCacheFile(path, filename, mc, data_hash):
     mcspec = ''