Fix missing GC root in interpreter.c

[Keno]

Static analysis complains in relevant part:

/home/keno/julia-1.0/src/interpreter.c:154:9: warning: Argument value may have been GCed
        jl_set_datatype_super(dt, super);
        ^
/home/keno/julia-1.0/src/interpreter.c:144:10: note: Started tracking value here
    dt = jl_new_abstracttype(name, modu, NULL, (jl_svec_t*)para);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/keno/julia-1.0/src/interpreter.c:146:23: note: Value may have been GCed here
    jl_binding_t *b = jl_get_binding_wr(modu, (jl_sym_t*)name, 1);
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/keno/julia-1.0/src/interpreter.c:154:9: note: Argument value may have been GCed
        jl_set_datatype_super(dt, super);
        ^                     ~~

Seems true to me. Add dt to the roots in this function. I thought we had already done this and indeed we covered similar cases in #25122, but this one seems to have been forgotten.

[yuyichao]

Seems valid.
Seems that moving the jl_get_binding_wr up is another possible fix?

[Keno]

Seems that moving the jl_get_binding_wr up is another possible fix?

Yeah, but try explaining how that rooting works to the static analyzer ;)

[Keno]

Also, I just pushed another fix here in the same file.

[yuyichao]

try explaining how that rooting works to the static analyzer

already explained it to you? ;-p

just pushed another fix here in the same file.

Looks good.