[Bug target/110011] -mfull-toc (-mfp-in-toc) yields incorrect _Float128 constants on power9

[vincent-gcc at vinc17 dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110011

--- Comment #4 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Kewen Lin from comment #3)
> Thanks for reporting, this exposes one issue that: when encoding KFmode
> constant into toc, it uses the format for the current long double, it could
> be wrong if the current long double is with IBM format instead of IEEE
> format. I have a patch.

OK, but why does an explicit `-mfull-toc` make this issue appear while this is
documented to be the default?