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/runtime/memtrack.c

@@ -171,7 +171,8 @@ noasan int ReleaseMemoryIntervals(struct MemoryIntervals *mm, int x, int y,
 }
 
 noasan int TrackMemoryInterval(struct MemoryIntervals *mm, int x, int y, long h,
-                               int prot, int flags, long offset, long size) {
+                               int prot, int flags, bool readonlyfile,
+                               bool iscow, long offset, long size) {
   /* asan runtime depends on this function */
   unsigned i;
   assert(y >= x);
@@ -197,6 +198,8 @@ noasan int TrackMemoryInterval(struct MemoryIntervals *mm, int x, int y, long h,
     mm->p[i].flags = flags;
     mm->p[i].offset = offset;
     mm->p[i].size = size;
+    mm->p[i].iscow = iscow;
+    mm->p[i].readonlyfile = readonlyfile;
   }
   return 0;
 }