D lang: cross-compile with Druntime + Phobos2

[kassane]

Currently, the available example, it can be seen that non-native build only -betterC mode is supported. (This is not on purpose - I'm not anti-GC).

Based on an experiment using meson (by @denizzzka). I ported to zig-build (with ABS), however the version used did not yet support cross-compilation in D, which had already been corrected previously.

• ldc2-druntime - zig build/gist

To guarantee this possibility, you would need to obtain access to the source code of Druntime and Phobos2, both standalone.
In the case of fortran-runtime (current release already available) is builded using zig c++ and included on:

anotherBuildStep/toolchains/flang.zig

Lines 176 to 184 in a1f40f9

	if (options.runtime) {
	const flang_dep = buildFortranRuntime(b, .{
	.target = options.target,
	.optimize = options.optimize,
	});
	flang_exec.addArtifactArg(flang_dep.artifact("FortranRuntime"));
	flang_exec.addArtifactArg(flang_dep.artifact("FortranDecimal"));
	flang_exec.addArtifactArg(flang_dep.artifact("Fortran_main"));
	}

[kassane]

PoC: https://github.com/kassane/druntime-zigbuild

• D runtime: Targets issues druntime-zigbuild#1