[pmc] simplify more mark methods

get the data once, and access the fields directly.
shorter and more cache friendly
[gc] add missing PackFileView to continuation.mark

also simplify the code a bit
[pmc] add Coroutine.mark with caller_seg

Coroutine.mark was just calling Sub.mark and missed to mark
the caller_seg. Do it now properly with inheritance.
Note that this does not fix GH #1109, which is a Coro in a wrong gen
[cage] unconst IO_VTABLE * vtables, -Wcast-qual cannot be suppressed

see e.g. https://stackoverflow.com/questions/13249756/explicit-ignore-warning-from-wcast-qual-cast-discards-attribute-const#comment38552597_13253997

2 remaining -Wcast-qual warnings for legacy API.
[test gc] add real gc stress tests #1108

stress test all GCs, under tight memory --gc-nursery-size=0.0001
and additional --gc-debug runs, with additonal StringBuilder stress via -t
and check the exit codes.
Properly fix SIGNAL detection and error output in Parrot::Test for exit_code_is.
Fails 14/20 tests.

t/harness: add existing TEST_PROG_ARGS to tests single tests, e.g.
  ulimit -Sv 60000
  TEST_PROG_ARGS='--gc-nursery-size=0.05 ' perl t/harness --gc-debug t/pmc/*.t
[config] improve auto::inline, uninitialized $test

and better --verbose return value
[gc] initialize more stack-allocated ptrs

see GH #1067.
initialize more values on the C-stack to help the GC.
also change some mem_internal_* to mem_sys_*
mem_internal_* are only macros to mem_sys now.

testcase:
  valgrind --track-origins=yes ./parrot_old examples/benchmarks/dispatch.pir

There's still a remaining stack-object scanned,
int offset from runops(src/call/ops.c),
which can only be fixed with a precise GC.
[core] initialize stackvars in Parrot_ext_call

we do not have a precise GC yet
[test] improve gc stress test

use pir not pasm,
print cmdline when failing
ChangeLog for smoke-me/valgrind-stack-gh1067