Allow codemodel and relocmodel to be optional when creating target machine

[sklam]

Change

llvmlite/ffi/targets.cpp

Lines 167 to 231 in ebc4c59

	API_EXPORT(LLVMTargetMachineRef)
	LLVMPY_CreateTargetMachine(LLVMTargetRef T,
	const char *Triple,
	const char *CPU,
	const char *Features,
	int OptLevel,
	const char *RelocModel,
	const char *CodeModel,
	int EmitJITDebug,
	int PrintMC)
	{
	using namespace llvm;
	CodeGenOpt::Level cgol;
	switch(OptLevel) {
	case 0:
	cgol = CodeGenOpt::None;
	break;
	case 1:
	cgol = CodeGenOpt::Less;
	break;
	case 3:
	cgol = CodeGenOpt::Aggressive;
	break;
	case 2:
	default:
	cgol = CodeGenOpt::Default;
	}
	CodeModel::Model cm;
	std::string cms(CodeModel);
	if (cms == "small")
	cm = CodeModel::Small;
	else if (cms == "kernel")
	cm = CodeModel::Kernel;
	else if (cms == "medium")
	cm = CodeModel::Medium;
	else if (cms == "large")
	cm = CodeModel::Large;
	else if (cms == "default") // As per LLVM 5, needed for AOT
	cm = CodeModel::Small;
	else { // catches "jitdefault" and not set, as per LLVM 5, needed for MCJIT
	// fall through, use model based on bitness
	int bits = sizeof(void *);
	if (bits == 4)
	cm = CodeModel::Small;
	else
	cm = CodeModel::Large;
	}
	Optional<Reloc::Model> rm;
	std::string rms(RelocModel);
	if (rms == "static")
	rm = Reloc::Static;
	else if (rms == "pic")
	rm = Reloc::PIC_;
	else if (rms == "dynamicnopic")
	rm = Reloc::DynamicNoPIC;
	TargetOptions opt;
	// opt.JITEmitDebugInfo = EmitJITDebug;
	opt.PrintMachineCode = PrintMC;
	return wrap(unwrap(T)->createTargetMachine(Triple, CPU, Features, opt,
	rm, cm, cgol));
	}

to accept optional codemodel and relocmodel. The createTagetMachine now takes them as Optional in
http://llvm.org/doxygen/classllvm_1_1Target.html#a3a99d5ba8f023d04d34f652af7494b35.
This will simplify the targetmachine creation process as codemodel and relocmodel is set differently of different platform.
Thus, avoiding the need of code like: https://github.com/numba/numba/pull/3437/files#diff-ec37b531d0f5e6e4ff2bb91a63bd651dR800

[sklam]

Related issue: #457 (comment)