ability to create import libs from def files without LLVM

[andrewrk]

Here we have a dependency on

zig/src/mingw.zig

Lines 413 to 417 in 8457439

	if (llvm_bindings.WriteImportLibrary(def_final_path_z.ptr, arch_tag, lib_final_path_z.ptr, true)) {
	// TODO surface a proper error here
	log.err("unable to turn {s}.def into {s}.lib", .{ lib_name, lib_name });
	return error.WritingImportLibFailed;
	}

which ultimately calls into this code:

zig/src/zig_llvm.cpp

Lines 988 to 1065 in 8457439

	bool ZigLLVMWriteImportLibrary(const char *def_path, const ZigLLVM_ArchType arch,
	const char *output_lib_path, bool kill_at)
	{
	COFF::MachineTypes machine = COFF::IMAGE_FILE_MACHINE_UNKNOWN;
	switch (arch) {
	case ZigLLVM_x86:
	machine = COFF::IMAGE_FILE_MACHINE_I386;
	break;
	case ZigLLVM_x86_64:
	machine = COFF::IMAGE_FILE_MACHINE_AMD64;
	break;
	case ZigLLVM_arm:
	case ZigLLVM_armeb:
	case ZigLLVM_thumb:
	case ZigLLVM_thumbeb:
	machine = COFF::IMAGE_FILE_MACHINE_ARMNT;
	break;
	case ZigLLVM_aarch64:
	case ZigLLVM_aarch64_be:
	machine = COFF::IMAGE_FILE_MACHINE_ARM64;
	break;
	default:
	break;
	}
	if (machine == COFF::IMAGE_FILE_MACHINE_UNKNOWN) {
	return true;
	}
	auto bufOrErr = MemoryBuffer::getFile(def_path);
	if (!bufOrErr) {
	return false;
	}
	MemoryBuffer& buf = *bufOrErr.get();
	Expected<object::COFFModuleDefinition> def =
	object::parseCOFFModuleDefinition(buf, machine, /* MingwDef */ true);
	if (!def) {
	return true;
	}
	// The exports-juggling code below is ripped from LLVM's DllToolDriver.cpp
	// If ExtName is set (if the "ExtName = Name" syntax was used), overwrite
	// Name with ExtName and clear ExtName. When only creating an import
	// library and not linking, the internal name is irrelevant. This avoids
	// cases where writeImportLibrary tries to transplant decoration from
	// symbol decoration onto ExtName.
	for (object::COFFShortExport& E : def->Exports) {
	if (!E.ExtName.empty()) {
	E.Name = E.ExtName;
	E.ExtName.clear();
	}
	}
	if (machine == COFF::IMAGE_FILE_MACHINE_I386 && kill_at) {
	for (object::COFFShortExport& E : def->Exports) {
	if (!E.AliasTarget.empty() || (!E.Name.empty() && E.Name[0] == '?'))
	continue;
	E.SymbolName = E.Name;
	// Trim off the trailing decoration. Symbols will always have a
	// starting prefix here (either _ for cdecl/stdcall, @ for fastcall
	// or ? for C++ functions). Vectorcall functions won't have any
	// fixed prefix, but the function base name will still be at least
	// one char.
	E.Name = E.Name.substr(0, E.Name.find('@', 1));
	// By making sure E.SymbolName != E.Name for decorated symbols,
	// writeImportLibrary writes these symbols with the type
	// IMPORT_NAME_UNDECORATE.
	}
	}
	return static_cast<bool>(
	object::writeImportLibrary(def->OutputFile, output_lib_path,
	def->Exports, machine, /* MinGW */ true));
	}

which is using the LLVM C++ API.

Instead, the zig compiler needs to directly support creating import libraries from .def files in order to eliminate this dependency on LLVM.