msun: expose the C23 functions we already support in <math.h>

[fuz]

Summary

This is the *pi family of trigonometric functions. Quite a few C23
functions are still missing. These seem to be:
acospi, acospif, acospil, asinpi, asinpif, asinpil, atan2pi, atan2pif,
atan2pil, atanpi, atanpif, atanpil, canonicalize, canonicalizef,
canonicalizel, compoundn, compoundnf, compoundnl, daddl, ddivl, dfmal,
dmull, dsqrtl, dsubl, exp10, exp10f, exp10l, exp10m1, exp10m1f,
exp10m1l, exp2m1, exp2m1f, exp2m1l, fadd, faddl, fdiv, fdivl, ffma,
ffmal, fmaximum, fmaximum_mag, fmaximum_mag_num, fmaximum_mag_numf,
fmaximum_mag_numl, fmaximum_magf, fmaximum_magl, fmaximum_num,
fmaximum_numf, fmaximum_numl, fmaximumf, fmaximuml, fminimum,
fminimum_mag, fminimum_mag_num, fminimum_mag_numf, fminimum_mag_numl,
fminimum_magf, fminimum_magl, fminimum_num, fminimum_numf,
fminimum_numl, fminimumf, fminimuml, fmul, fmull, fromfp, fromfpf,
fromfpl, fromfpx, fromfpxf, fromfpxl, fsqrt, fsqrtl, fsub, fsubl,
iscanonical, iseqsig, issignaling, issubnormal, iszero, nextdown,
nextdownf, nextdownl, nextup, nextupf, nextupl, pown, pownf, pownl,
powr, powrf, powrl, rootf, rootl, rootn, roundeven, roundevenf,
roundevenl, rsqrt, rsqrtf, rsqrtl, ufromfp, ufromfpf, ufromfpl,
ufromfpx, ufromfpxf, ufromfpxl.

Test Plan

n/a

[fuz]

• msun/man: use new -ieee754-2008 macro in *pi.3

[fuz]

• msun/man: bump date in tanpi.3

[markj]

Approved.