[Bug c/77530] optimization prevents excess precision from being removed with x86/amd64 long double and rounding to 53 bits

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77530

--- Comment #3 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
More precisely, up to NetBSD 6, it is 53 bits (gcc70 is NetBSD 5.1). As of
NetBSD 7, it is 64 bits.