Perform some code maintenance

- Change IDT code so kprintf() isn't mandatory dependency
- Document current intentions around pthread_cancel()
- Make _npassert() an _unassert() in MODE=tiny

libc/assert.h

@@ -2,7 +2,6 @@
 #define COSMOPOLITAN_LIBC_ASSERT_H_
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
-#include "libc/intrin/kprintf.h"
 
 extern bool __assert_disable;
 void __assert_fail(const char *, const char *, int) hidden relegated;
@@ -24,13 +23,16 @@ void __assert_fail(const char *, const char *, int) hidden relegated;
     }                                \
   } while (0)
 
-#define _npassert(x)                                  \
-  do {                                                \
-    if (__builtin_expect(!(x), 0)) {                  \
-      kprintf("%s:%d: oh no!\n", __FILE__, __LINE__); \
-      notpossible;                                    \
-    }                                                 \
+#ifndef TINY
+#define _npassert(x)                 \
+  do {                               \
+    if (__builtin_expect(!(x), 0)) { \
+      notpossible;                   \
+    }                                \
   } while (0)
+#else
+#define _npassert(x) _unassert(x)
+#endif
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */