Improve mkdeps

Our makefile generator now accepts badly formatted include lines. It's
now more hermetic with better error checking in the cosmo repo, and it
can be configured to not be hermetic at all.

libc/intrin/cxalock.c

@@ -33,7 +33,10 @@ void __cxa_unlock(void) {
   pthread_mutex_unlock(&__cxa_lock_obj);
 }
 
-__attribute__((__constructor__)) static void __cxa_init(void) {
-  __cxa_wipe();
+static textstartup void __cxa_init() {
   pthread_atfork(__cxa_lock, __cxa_unlock, __cxa_wipe);
 }
+
+const void *const __cxa_ctor[] initarray = {
+    __cxa_init,
+};