Some comparison with D:
> Do I have access to an asm keyword,
Yes, D has a builtin assembler
> or can I easily link assembly files?
Yes
> Do I have access to the linker phase to customize the layout of the ELF file?
D uses standard linkers.
> Does it need a runtime to work?
With the -betterC switch, it only relies on the C runtime
> Can I disable the standard library?
You don't need the C runtime if you don't call any of the functions in it.