[Bug bootstrap/90418] [10 Regression] powerpc-darwin9 bootstrap fails after r271013

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90418

--- Comment #7 from Iain Sandoe <iains at gcc dot gnu.org> ---
Created attachment 46340
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46340&action=edit
Patch under test

This is a combination of Jakub's patch
https://gcc.gnu.org/ml/gcc-patches/2019-05/msg00484.html

+ a fragment to note that WORLD_SAVE_P is set in -mdebug=stack

+ change to rs6000_function_ok_for_sibcall to return false for eh_return cases.