Makefile: -fuse-ld argument is not resulting in the linker provided by the 'LD' environment variable being used

[ArthurHeymans]

If an external linker is provided with the 'LD' environment flag, the Makefile will only guess if it is LLD or BFD type, rather than passing the linker to the -fuse-ld argument. If cross compiling this might result in the host linker being used which might not support risc-v.