Incremental build is broken

[Jakub Jermář]

Incremental build is severely broken. Steps to reproduce:

1. build default amd64 profile
2. apply the patch below that should result in HelenOS hanging early during boot
3. type make and watch how only libc gets rebuilt
4. run HelenOS and watch how HelenOS continues to build
5. now do make clean; make
6. only now the change takes effect and HelenOS hangs as expected

The patch for testing:

diff --git a/uspace/lib/c/generic/async/server.c b/uspace/lib/c/generic/async/server.c
index a75825b1e..41e02f78f 100644
--- a/uspace/lib/c/generic/async/server.c
+++ b/uspace/lib/c/generic/async/server.c
@@ -1024,6 +1024,7 @@ void __async_server_init(void)
 
 errno_t async_accept_0(ipc_call_t *call)
 {
+       for(;;);
        return ipc_answer_5(call->cap_handle, EOK, 0, 0, 0, 0,
            async_get_label());
 }