Add return scope to realloc

[dkorpel]

Split off from #8113
Since realloc could return the input if there is enough capacity, it should be return scope. While in practice realloc is all @system and @trusted code, it does seem to trip up issue 20150.

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[dkorpel]

Turns out that std.internal.cstring: tempCString is tricky, since it dynamically switches between stack and heap memory, which trips up scope.

[dkorpel]

Turns out that std.internal.cstring: tempCString is tricky, since it dynamically switches between stack and heap memory, which trips up scope.

I now split up the stack-logic and heap-logic into two functions, so that the former can be scope while the latter return scope.

[RazvanN7]

Please rebase to restart circleCI

[wilzbach]

@RazvanN7 maybe you could rebase for the author? The ping, rebase, wait for auto-merge label to be re-added cycle seems a bit inefficient.

[RazvanN7]

@wilzbach Of course I can do the rebase myself, however, I think it's better to keep the PR author engaged.

[dkorpel]

@wilzbach Of course I can do the rebase myself, however, I think it's better to keep the PR author engaged.

Having to rebase my PRs over and over again because of CI issues is not very engaging though 😬