MFC r321456,r321484,r321486:

r321456:

Convert lib/msun/trig_test from TAP to ATF format

Only expose :accuracy and :reduction if !i386, similar to before,
but more holistically to avoid future -Wunused issue with the unused
functions.

r321484:

Only test ld_pi_odd with LDBL_MANT_DIG == 64 to fix the build

The empty (unimplemented) test inputs for sparc64 trigger a -Wtype-limits build
failure because nitems of an empty array is always false, i.e., deadcode.

MFC with: r321455

r321486:

Re-add #endif accidentally deleted in r321484

MFC with: r321455, r321484