add support for --image-base to self-hosted linking

[andrewrk]

1d777e9 added support for --image-base (see #6121) however it only added support when linking with LLD - not for the self-hosted linker code. This issue is to either (1) additionally add support for image base to ELF and COFF linking, or (2) decide that it will not be supported. We have logic to require LLD linking when this option is selected:

zig/src/Compilation.zig

Lines 438 to 460 in 1d777e9

	// Make a decision on whether to use LLD or our own linker.
	const use_lld = if (options.use_lld) |explicit| explicit else blk: {
	if (!build_options.have_llvm)
	break :blk false;
	if (ofmt == .c)
	break :blk false;
	// Our linker can't handle objects or most advanced options yet.
	if (options.link_objects.len != 0 or
	options.c_source_files.len != 0 or
	options.frameworks.len != 0 or
	options.system_libs.len != 0 or
	options.link_libc or options.link_libcpp or
	options.link_eh_frame_hdr or
	options.link_emit_relocs or
	options.output_mode == .Lib or
	options.lld_argv.len != 0 or
	options.image_base_override != null or
	options.linker_script != null or options.version_script != null)
	{
	break :blk true;
	}