[Bug target/83862] powerpc: ICE in signbit testcase

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83862

--- Comment #4 from Michael Meissner <meissner at gcc dot gnu.org> ---
GCC 6 backport applied, GCC 7 backport waiting for GCC 7.3 to ship, before
applying the patch.