[PATCH] D95915: [clang][driver] Only warn once about invalid -stdlib value

[Timm Bäder via Phabricator via cfe-commits]

tbaeder added a comment.

In D95915#2541129 <https://reviews.llvm.org/D95915#2541129>, @Hahnfeld wrote:

> My proposal would be to cache the return value of the three routines in `ToolChain`. This has the advantage that the values get parsed only once and there is at most one warning. I don't know how this plays with parallelization efforts, but I don't think we should worry about this right now, given the current code.

That's what I was looking at right now as well, since using `std::call_once()` already means the methods can't be `const` anymore anyway. Might as well just cache the value. It is still slightly ugly with the current code in that subclasses can override them and then the caching is gone.


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