Run interprocedural const prop before global optimizer

Run interprocedural const prop before global optimizer

Exposes more constant globals that can be removed by
the global optimizer. A specific example is the removal
of the static global block address array in
clang/test/CodeGen/indirect-goto.c. This change impacts only
lower optimization levels. With LTO interprocedural
const prop runs already before global opt.

llvm-svn: 212284