[build] Add build knowledge of dynamic libraries

Bonnibel will now build dynamic libraries when they're dependencies for
non-statically linked modules. It will also copy those shared libraries
into the initrd image for programs being copied into the image.

src/user/srv.init/init.module

@@ -3,6 +3,7 @@
 init = module("srv.init",
     targets = [ "init" ],
     deps = [ "libc", "elf", "bootproto", "zstd" ],
+    static = True,
     description = "Init server",
     ld_script = "init.ld",
     sources = [