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/lockcmpxchg.h

@@ -0,0 +1,29 @@
+#ifndef COSMOPOLITAN_LIBC_INTRIN_LOCKCMPXCHG_H_
+#define COSMOPOLITAN_LIBC_INTRIN_LOCKCMPXCHG_H_
+#include "libc/bits/asmflag.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+bool _lockcmpxchg(void *, intptr_t, intptr_t, size_t);
+
+#if defined(__GNUC__) && !defined(__STRICT_ANSI__) && defined(__x86__)
+#define _lockcmpxchg(IFTHING, ISEQUALTOME, REPLACEITWITHME)                   \
+  ({                                                                          \
+    bool DidIt;                                                               \
+    autotype(IFTHING) IfThing = (IFTHING);                                    \
+    typeof(*IfThing) IsEqualToMe = (ISEQUALTOME);                             \
+    typeof(*IfThing) ReplaceItWithMe = (REPLACEITWITHME);                     \
+    asm volatile(ZFLAG_ASM("lock cmpxchg\t%3,%1")                             \
+                 : ZFLAG_CONSTRAINT(DidIt), "+m"(*IfThing), "+a"(IsEqualToMe) \
+                 : "r"(ReplaceItWithMe)                                       \
+                 : "cc");                                                     \
+    DidIt;                                                                    \
+  })
+#else
+#define _lockcmpxchg(MEM, CMP, VAL) \
+  _lockcmpxchg(MEM, (intptr_t)(CMP), (intptr_t)(VAL), sizeof(*(MEM)))
+#endif /* GNUC && !ANSI && x86 */
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_INTRIN_LOCKCMPXCHG_H_ */