epp learned to handle the -warning() directive in 14d72f02, but
make and ct_make were not updated to expect a {warning,_} return
value from epp:parse_erl_form/1.

Ensure that we cannot get any dangling pointers into code that
has been purged. This is done by a two phase purge. At first
phase all fun entries pointing into the code to purge are marked
for purge. All processes trying to call these funs will be suspended
and by this we avoid getting new direct references into the code.
When all processes has been checked, these processes are resumed.

The new purge strategy now also completely ignore the existence of
indirect references to the code (funs). If such exist, they will
cause bad fun exceptions to the caller, but will not prevent a
soft purge or cause a kill of a process having such live references
during a hard purge. This since it is impossible to give any
guarantees that no processes in the system have such indirect
references. Even when the system is completely clean from such
references, new ones can appear via distribution and/or disk.

The bug when introduced in OTP-19.0.

Optimize adding multiple modules to an Xref server

OTP-13499

* egil/tools/modernize-tests:
  tools: Don't divide by zero in tests
  Fix instruments_SUITE sumblock check
  Eliminate use of doc and suite clauses
  Replace ?t with test_server
  Use test_server:is_debug/0 instead of custom check
  Replace use of test_server:format/2 with io:format/2
  Eliminate use of ?config() macro
  Eliminate use of test_server:fail/0,1
  Eliminate erlang:now/0
  Modernize use of timetraps
  Remove ?line macros

Those clause are obsolete and never used by common_test.