Improve locks and signals

- Introduce fast spinlock API
- Double rand64() perf w/ spinlock
- Improve raise() on New Technology
- Support gettid() across platforms
- Implement SA_NODEFER on New Technology
- Move the lock intrinsics into LIBC_INTRIN
- Make SIGTRAP recoverable on New Technology
- Block SIGCHLD in wait4() on New Technology
- Add threading prototypes for XNU and FreeBSD
- Rewrite abort() fixing its minor bugs on XNU/NT
- Shave down a lot of the content in libc/bits/bits.h
- Let signal handlers modify CPU registers on New Technology

libc/intrin/spinlock.h

@@ -0,0 +1,22 @@
+#ifndef COSMOPOLITAN_LIBC_INTRIN_SPINLOCK_H_
+#define COSMOPOLITAN_LIBC_INTRIN_SPINLOCK_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+/* "Place each synchronization variable alone,
+    separated by 128 bytes or in a separate cache line."
+                   ──Intel Optimization Manual §8.3.1 */
+struct cthread_spinlock_t {
+  bool x;
+  int owner;
+  char __ignore[128 - 1 - 4];
+} forcealign(128);
+
+typedef struct cthread_spinlock_t cthread_spinlock_t;
+
+void cthread_spinlock(cthread_spinlock_t *) dontthrow;
+void cthread_spunlock(cthread_spinlock_t *) dontthrow;
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_INTRIN_SPINLOCK_H_ */