Make more fixes and improvements

- Remove PAGESIZE constant
- Fix realloc() documentation
- Fix ttyname_r() error reporting
- Make forking more reliable on Windows
- Make execvp() a few microseconds faster
- Make system() a few microseconds faster
- Tighten up the socket-related magic numbers
- Loosen restrictions on mmap() offset alignment
- Improve GetProgramExecutableName() with getenv("_")
- Use mkstemp() as basis for mktemp(), tmpfile(), tmpfd()
- Fix flakes in pthread_cancel_test, unix_test, fork_test
- Fix recently introduced futex stack overflow regression
- Let sockets be passed as stdio to subprocesses on Windows
- Improve security of bind() on Windows w/ SO_EXCLUSIVEADDRUSE

libc/intrin/printmemoryintervals.c

@@ -27,7 +27,6 @@ static bool IsNoteworthyHole(unsigned i, const struct MemoryIntervals *mm) {
   // gaps between shadow frames aren't interesting
   // the chasm from heap to stack ruins statistics
   return !(
-      (IsArenaFrame(mm->p[i].y) && !IsArenaFrame(mm->p[i + 1].x)) ||
       (IsShadowFrame(mm->p[i].y) || IsShadowFrame(mm->p[i + 1].x)) ||
       (!IsStaticStackFrame(mm->p[i].y) && IsStaticStackFrame(mm->p[i + 1].x)));
 }