* Remove all functions and a number of constants that neither
glibc nor musl define or support (and even FreeBSD does not
declare a good number of these anymore.)
* Redeclare the primary flags in terms of (1 << X) instead
of raw 0x... for readability (the constants at the end
do NOT match up to their definitions in glibc, musl, and BSDs!)
* Remove usage of unneeded headers, and __BEGIN/END_DECLS.
* Replace non-Haiku license headers with the ones from FreeBSD,
which notably contain a removal of the advertising clause.
ABIs remain unchanged, but a small set of applications that
use these esoteric APIs may not compile anymore (are there
any remaining?)
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