`isdefinedglobal` doc string needs a compat annotation for v1.12

[nsajko]

It doesn't seem to be available on v1.11, v1.10 or v1.9.

[jakobnissen]

Note sure I understand:

julia> VERSION
v"1.10.9"

julia> isdefined(Base, :prod)
true

Is it a certain method that's not available?

[nsajko]

Sorry, I meant isdefinedglobal.