use @system to return pointers to stack

[WalterBright]

Another blocker for dlang/dmd#5972

[dlang-bot]

@WalterBright, thanks for your PR! By analyzing the annotation information on this pull request, we identified @jpf91, @jcd and @MartinNowak to be potential reviewers. @jpf91: The PR was automatically assigned to you, please reassign it if you were identified mistakenly.

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[codecov-io]

Current coverage is 88.79% (diff: 100%)

Merging #4750 into master will decrease coverage by <.01%

@@             master      #4750   diff @@
==========================================
  Files           121        121          
  Lines         74169      74169          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          65861      65860     -1   
- Misses         8308       8309     +1   
  Partials          0          0          

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[dnadlinger]

Isn't this @system by default?

[andralex]

annotation is informative nevertheless

[dnadlinger]

@andralex: Nonononono - Walter says this is a blocker, so it apparently isn't just informative with his proposed changes (?).

[andralex]

@WalterBright?