[Bug libstdc++/87635] backport of cmath patches to gcc 48 for Darwin incomplete cmath

[rm at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87635

--- Comment #2 from Riccardo <rm at gnu dot org> ---
Just for the reference, I backported the fix also to gcc 6.5
It applied almost cleanly.

Given your comment, I don't think it is worth opening a new bug just for that?
So I leave the patch here for the record.