fix issue 12330 - array.reserve at compile time too

[ghost]

makes reserve() a noop at compile-time allowing to CTFE

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	12330	enhancement	array.reserve at compile time too

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + druntime#2532"