[Bug target/64580] very high rs6000_stack_info() usage during LTO Firefox build on ppc64

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64580

--- Comment #12 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Fixed for gcc-5. Many thanks.
I'll leave this bug open for possible backports.