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

ape/loader.c

@@ -438,16 +438,6 @@ static long Write(int fd, const void *data, unsigned long size, int os) {
   return CallSystem(fd, (long)data, size, 0, 0, 0, 0, numba, os);
 }
 
-static int Execve(const char *prog, char **argv, char **envp, int os) {
-  int numba;
-  if (IsLinux() && IsAarch64()) {
-    numba = 221;
-  } else {
-    numba = 59;
-  }
-  return CallSystem((long)prog, (long)argv, (long)envp, 0, 0, 0, 0, numba, os);
-}
-
 static int Access(const char *path, int mode, int os) {
   if (IsLinux() && IsAarch64()) {
     return SystemCall(-100, (long)path, mode, 0, 0, 0, 0, 48);