[libc][i386] FPBit support for 96b long double (#115084)
`long double` is haunted on most architectures, but it is especially so on
i386-linux-gnu. While have 80b of significant data, on i386-linux-gnu this type
has 96b of storage.
Fixes for supporting printf family of conversions for `long double` on
i386-linux-gnu. This allows the libc-stdlib-tests and libc_stdio_unittests
ninja target tests to pass on i386-linux-gnu.
Fixes: #110894
Link: #93709
Co-authored-by: Michael Jones <michaelrj@google.com>
