Run SimplifyLibCalls near the beginning, not at

the end.  It is now run at the same moment as in
llvm-gcc.  Also, run StripDeadPrototypes at the
end, just before running DeadTypeElimination.
This may be useful when doing LTO.  Note that
llvm-gcc runs StripDeadPrototypes but not
DeadTypeElimination.

llvm-svn: 49848