[Docs] add note to avoid 'errno' for better vectorization (PR40265)

This is a partial fix for the documentation improvements requested in:
https://bugs.llvm.org/show_bug.cgi?id=40265


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350845 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed