Do not set errno for overflowing NaN payload in strtod/nan (bug 32045)

Do not set errno for overflowing NaN payload in strtod/nan (bug 32045)

As reported in bug 32045, it's incorrect for strtod/nan functions to
set errno based on overflowing payload (strtod should only set errno
for overflow / underflow of its actual result, and potentially if
nothing in the string can be parsed as a number at all; nan should be
a pure function that never sets it).  Save and restore errno around
the internal strtoull call and add associated test coverage.

Tested for x86_64.