Rename argument strings of codegen passes to avoid collisions with command line
options.

This commit changes the command line arguments (PassInfo::PassArgument) of two
passes, MachineFunctionPrinter and MachineScheduler, to avoid collisions with
command line options that have the same argument strings.

This bug manifests when the PassList construct (defined in opt.cpp) is used
in a tool that links with codegen passes. To reproduce the bug, paste the
following lines into llc.cpp and run llc.

#include "llvm/IR/LegacyPassNameParser.h"
static llvm::cl::list<const llvm::PassInfo*, bool, llvm::PassNameParser>
PassList(llvm::cl::desc("Optimizations available:"));

rdar://problem/19212448