Improve synchronization

- Fix bugs in kDos2Errno definition
- malloc() should now be thread safe
- Fix bug in rollup.com header generator
- Fix open(O_APPEND) on the New Technology
- Fix select() on the New Technology and test it
- Work towards refactoring i/o for thread safety
- Socket reads and writes on NT now poll for signals
- Work towards i/o completion ports on the New Technology
- Make read() and write() intermittently check for signals
- Blinkenlights keyboard i/o so much better on NT w/ poll()
- You can now poll() files and sockets at the same time on NT
- Fix bug in appendr() that manifests with dlmalloc footers off

libc/rand/rand64.c

@@ -31,7 +31,7 @@
 extern int __pid;
 static int thepid;
 static uint128_t thepool;
-static cthread_spinlock_t rand64_lock;
+_Alignas(64) static char rand64_lock;
 
 /**
  * Returns nondeterministic random data.
@@ -54,7 +54,7 @@ static cthread_spinlock_t rand64_lock;
 uint64_t rand64(void) {
   void *p;
   uint128_t s;
-  cthread_spinlock(&rand64_lock);
+  _spinlock(&rand64_lock);
   if (__pid == thepid) {
     s = thepool;  // normal path
   } else {
@@ -75,6 +75,6 @@ uint64_t rand64(void) {
     thepid = __pid;
   }
   thepool = (s *= 15750249268501108917ull);  // lemur64
-  cthread_spunlock(&rand64_lock);
+  _spunlock(&rand64_lock);
   return s >> 64;
 }