[gc] prettier GC memory statistics for GMS with -D1
pbc_to_exe: static char execname[1024]
[gc] fix the Coroutine GC bug #1108

 Coroutine.clone needs to reset the GC flags
[pmc] improve Coroutine.init

call SUPER
temp: unroll more POINTER_ARRAY_ITER macros
trace: protect from empty StringBuilder