[Bug tree-optimization/63960] [meta-bug] Port tail-merge fixes to 4.8

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63960

--- Comment #1 from vries at gcc dot gnu.org ---
- Fix PR64091
  https://gcc.gnu.org/ml/gcc-patches/2014-11/msg03397.html