doc: Mention <math.h> function that were added in ISO C23.
* doc/posix-functions/acospi.texi: New file.
* doc/posix-functions/acospif.texi: New file.
* doc/posix-functions/acospil.texi: New file.
* doc/posix-functions/asinpi.texi: New file.
* doc/posix-functions/asinpif.texi: New file.
* doc/posix-functions/asinpil.texi: New file.
* doc/posix-functions/atanpi.texi: New file.
* doc/posix-functions/atanpif.texi: New file.
* doc/posix-functions/atanpil.texi: New file.
* doc/posix-functions/atan2pi.texi: New file.
* doc/posix-functions/atan2pif.texi: New file.
* doc/posix-functions/atan2pil.texi: New file.
* doc/posix-functions/compoundn.texi: New file.
* doc/posix-functions/compoundnf.texi: New file.
* doc/posix-functions/compoundnl.texi: New file.
* doc/posix-functions/cospi.texi: New file.
* doc/posix-functions/cospif.texi: New file.
* doc/posix-functions/cospil.texi: New file.
* doc/posix-functions/exp10.texi: Moved here from doc/glibc-functions/.
* doc/posix-functions/exp10f.texi: Moved here from doc/glibc-functions/.
* doc/posix-functions/exp10l.texi: Moved here from doc/glibc-functions/.
* doc/posix-functions/exp10m1.texi: New file.
* doc/posix-functions/exp10m1f.texi: New file.
* doc/posix-functions/exp10m1l.texi: New file.
* doc/posix-functions/exp2m1.texi: New file.
* doc/posix-functions/exp2m1f.texi: New file.
* doc/posix-functions/exp2m1l.texi: New file.
* doc/posix-functions/log10p1.texi: New file.
* doc/posix-functions/log10p1f.texi: New file.
* doc/posix-functions/log10p1l.texi: New file.
* doc/posix-functions/log2p1.texi: New file.
* doc/posix-functions/log2p1f.texi: New file.
* doc/posix-functions/log2p1l.texi: New file.
* doc/posix-functions/logp1.texi: New file.
* doc/posix-functions/logp1f.texi: New file.
* doc/posix-functions/logp1l.texi: New file.
* doc/posix-functions/pown.texi: New file.
* doc/posix-functions/pownf.texi: New file.
* doc/posix-functions/pownl.texi: New file.
* doc/posix-functions/powr.texi: New file.
* doc/posix-functions/powrf.texi: New file.
* doc/posix-functions/powrl.texi: New file.
* doc/posix-functions/rootn.texi: New file.
* doc/posix-functions/rootnf.texi: New file.
* doc/posix-functions/rootnl.texi: New file.
* doc/posix-functions/rsqrt.texi: New file.
* doc/posix-functions/rsqrtf.texi: New file.
* doc/posix-functions/rsqrtl.texi: New file.
* doc/posix-functions/sinpi.texi: New file.
* doc/posix-functions/sinpif.texi: New file.
* doc/posix-functions/sinpil.texi: New file.
* doc/posix-functions/tanpi.texi: New file.
* doc/posix-functions/tanpif.texi: New file.
* doc/posix-functions/tanpil.texi: New file.
* doc/gnulib.texi (Function Substitutes): Include them.
(Glibc math.h): Don't include glibc-functions/exp10*.texi.