Add new libm LIBBUILTIN definitions, synchronizing with __builtin_*

For all libm __builtin_* functions that are defined, this adds the
corresponding LIBBUILTIN definitions (tagged, as necessary, with "e" instead of
"c" when the function may set errno).

Note that this changes the current definitions for lrint and fma
(unfortunately). The Linux man page documents that these don't set errno, but
the POSIX standard says that they should.