This discussion reminds me of one of my (numerous) pet peeves
about the glibc source tree.
If you want to figure out where something is implemented for a given
target, you have to walk through the tree like a monkey in some
prioritized list of directories to find the source file or header file
that glibc ends up using.
At least with what we're using now, you open up the file for ARCH and
you see the includes so you know exactly where to go.
So I think this "just provide no file to use default implementation"
might not be the best idea in the long term.
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