self-hosted: build against zig_llvm and embedded LLD

Now the self-hosted compiler re-uses the same C++ code for interfacing
with LLVM as the C++ code.
It also links against the same LLD library files.

src/codegen.cpp

@@ -17,7 +17,7 @@
 #include "os.hpp"
 #include "translate_c.hpp"
 #include "target.hpp"
-#include "zig_llvm.hpp"
+#include "zig_llvm.h"
 
 #include <stdio.h>
 #include <errno.h>