Add or1k-linux support (via CBE)

[alexrp]

Just a little weekend project to show how, using the CBE, support can be added for a target that we don't yet have a backend for:

❯ cat main.zig
const std = @import("std");
pub fn main() void {
    std.debug.print("hello world\n", .{});
}
❯ zig build-lib $ZIG/ziglang/zig/lib/compiler_rt.zig -target or1k-linux-gnu -lc -ofmt=c
❯ zig build-exe main.zig -target or1k-linux-gnu -lc -ofmt=c
❯ or1k-linux-gnu-gcc compiler_rt.c -I $ZIG/ziglang/zig/lib -std=gnu99 -c
❯ or1k-linux-gnu-gcc main.c -I $ZIG/ziglang/zig/lib -std=gnu99 compiler_rt.o
❯ qemu-or1k -L $LIBCS/or1k-linux-gnu-hard ./a.out
hello world