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/getauxval.c

@@ -35,7 +35,11 @@ unsigned long getauxval(unsigned long key) {
   x = _getauxval(key);
   if (key == AT_PAGESZ) {
     if (!x.isfound) {
+#ifdef __aarch64__
       x.value = 16384;
+#else
+      x.value = 4096;
+#endif
     }
     x.isfound = true;
   }