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-freebsd.internal.h

@@ -0,0 +1,39 @@
+#ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGINFO_FREEBSD_H_
+#define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGINFO_FREEBSD_H_
+#include "libc/calls/struct/sigval.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+struct siginfo_freebsd {
+  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;
+  union {
+    struct {
+      int32_t si_trapno;
+    };
+    struct {
+      int32_t si_timerid;
+      int32_t si_overrun;
+    };
+    struct {
+      int32_t si_mqd;
+    };
+    struct {
+      long si_band;
+    };
+    struct {
+      int64_t __pad1;
+      int32_t __pad2[7];
+    };
+  };
+};
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGINFO_FREEBSD_H_ */