[libj6] Move remaining j6 headers out of src/include

This means the kernel now depends on libj6. I've added the macro
definition __j6kernel when building for the kernel target, so I can
remove parts with #ifdefs.

src/libraries/j6/j6.module

@@ -5,10 +5,15 @@ j6 = module("j6",
     includes = [ "include" ],
     sources = [
         "init.cpp",
+        "include/j6/syscalls.h.cog",
+        "syscalls.s.cog",
     ])
 
 from glob import glob
 definitions = glob('definitions/**/*.def', recursive=True)
-j6.add_input("include/j6/syscalls.h.cog", deps=definitions)
-j6.add_input("syscalls.s.cog", deps=definitions)
+
+j6.add_depends([
+        "include/j6/syscalls.h.cog",
+        "syscalls.s.cog",
+    ], definitions)