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/lockxadd.h

@@ -0,0 +1,22 @@
+#ifndef COSMOPOLITAN_LIBC_BITS_LOCKXADD_H_
+#define COSMOPOLITAN_LIBC_BITS_LOCKXADD_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+intptr_t _lockxadd(void *, intptr_t, size_t);
+
+#if defined(__GNUC__) && !defined(__STRICT_ANSI__) && defined(__x86__)
+#define _lockxadd(PTR, VAL)                                                \
+  ({                                                                       \
+    typeof(*(PTR)) Res;                                                    \
+    typeof(Res) Val = (VAL);                                               \
+    asm volatile("lock xadd\t%0,%1" : "=r"(Res), "+m"(*(PTR)) : "0"(Val)); \
+    Res; /* contains *PTR before addition cf. InterlockedAdd() */          \
+  })
+#else
+#define _lockxadd(MEM, VAL) _lockxadd(MEM, (intptr_t)(VAL), sizeof(*(MEM)))
+#endif /* GNUC && !ANSI && x86 */
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_BITS_LOCKXADD_H_ */