Fix a behavioral change accidentally introduced by the move to the LLVM commandline system: `-output-(bc|ll|s)` used to disable generation of an object file unless explicitly requested with `-output-o`. Now they do so again.

#ifndef LDC_GEN_OPTIMIZER_H
#define LDC_GEN_OPTIMIZER_H

namespace llvm { class Module; }

bool ldc_optimize_module(llvm::Module* m);

bool doInline();

int optLevel();

bool optimize();

#endif