Implement another D-specific pass: -dgc2stack This one promotes GC allocations to stack memory when it can determine it's safe to do so. Not all GC calls are recognized yet (in fact only one *is* recognized for now). Needs metadata, so disabled for LLVM versions that don't support it.

// D runtime support helpers

bool LLVM_D_InitRuntime();
void LLVM_D_FreeRuntime();

llvm::Function* LLVM_D_GetRuntimeFunction(llvm::Module* target, const char* name);

llvm::GlobalVariable* LLVM_D_GetRuntimeGlobal(llvm::Module* target, const char* name);