Improve signals and memory protection

- Document sigaction()
- Simplify New Technology fork() code
- Testing and many bug fixes for mprotect()
- Distribute Intel Xed ILD in the amalgamation
- Turn Xed enums into defines to avoid DWARF bloat
- Improve polyfilling of SA_SIGINFO on BSDs and fix bugs
- setpgid(getpid(), getpid()) on Windows will ignore CTRL-C
- Work around issues relating to NT mappings being executable
- Permit automatic executable stack override via `ape_stack_pf`

libc/calls/struct/siginfo-xnu.internal.h

@@ -0,0 +1,22 @@
+#ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGINFO_XNU_H_
+#define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGINFO_XNU_H_
+#include "libc/calls/struct/sigval.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+struct siginfo_xnu {
+  int32_t si_signo;
+  int32_t si_errno;
+  int32_t si_code;
+  int32_t si_pid;
+  int32_t si_uid;
+  int32_t si_status;
+  void *si_addr;
+  union sigval si_value;
+  int64_t si_band;
+  uint64_t __pad[7];
+};
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGINFO_XNU_H_ */