Feature: self hosting prototype implemented

This is a large change. In order to remove myself from libc's arcane
interface, I implemented an independent runtime layer. It is based on
musl's wonderful implementation mostly. Critically, if libc is linked to
the program, then we cooperate. Namely, we call start main and let libc
do all initialization. If not, then we have a noop defined in rt3.a.

The general structure of the file is:
1. sys/$os/$arch contains all architecture dependent code
2. sys/$os/port contains all code that depends on the os, but is
   portable
3. rt/$arch contains all the runtime architecture dependent code
4. rt/* contains the portable runtime code.

Obviously testing is needed. Specifically, while code is checked in for
the most popular architectures, it only has been tested on one computer!
Overall this is exciting and as been educational.

1 files changed, 17 insertions, 5 deletions

diff --git a/sys/rt/exit.c b/sys/rt/exit.c
index 55a684a..e6027b7 100644
--- a/sys/rt/exit.c
+++ b/sys/rt/exit.c
@@ -1,15 +1,27 @@
+#include <u.h>
 #include <rt.h>
-#include <sys.h>
+#include <syscall.h>
 
-void
-rt·exit(int code)
+/* XXX:
+ * if we are here, we are in charge, call exit syscalls
+ * think of better way to encapsulate these syscalls?
+ */
+static noreturn void
+rt·shutdown(int code)
 {
     if(rt·context.fini)
         rt·context.fini();
     if(rt·context.exit)
         rt·context.exit();
 
-    /* call exit syscalls here */
+	_syscall1(·ExitGroup, code);
+    for(;;)
+		_syscall1(·Exit, code);
+}
+weakalias(rt·shutdown, exit);
 
-    for(;;);
+noreturn void
+rt·exit(int code)
+{
+	rt·shutdown(code);
 }