[PATCH] libstdc++: fix a dangling reference crash in ranges::is_permutation

[Giuseppe D'Angelo]

Hi,

The implementation of ranges::is_permutation may create a dangling 
reference, which then results (sometimes) in a crash. A minimal example 
that shows the problem under ASAN is https://gcc.godbolt.org/z/7bP9nE8fK

The attached patch fixes it. I've tested on Linux x86-64. Adding a 
negative test for this is somehow challenging (how do you test you're 
not using a dangling reference?), but running the modified test under 
ASAN shows the fix in place.

Do you need me to create a report on bugzilla and cross-reference it 
from the patch?

Thanks,
-- 
Giuseppe D'Angelo
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