[Bug target/112993] rs6000: Rework precision for 128bit float types and modes

[linkw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112993
Bug 112993 depends on bug 116170, which changed state.

Bug 116170 Summary: [15 regression] ICE unrecognizable insn since 
r15-2084-g33dca0a4c1c421
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116170

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED