Add more 'fail'ing TD callgraph tests.

* addrtaken tests, previously committed.
  (based on tests from Victor van der Veen, thanks!)
* 'decode' testcase from mailing list.
  (based on example from Maxim Olifer, thanks!)

These are tests of callgraph precision that
currently fail.  Marking XFAIL (like test in the previous commit)
until can convince myself/others of what the
correct behavior is.

llvm-svn: 238490
3 files changed