std.mem.Allocator: fix not passing return_address
std.mem.Allocator: fix not passing return_address

This makes collected stack traces omit less useful frames. For user
applications which only store a fixed number of stack frames this can
make a big difference.

raulgrell/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig