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/kprintf.greg.c

@@ -625,7 +625,7 @@ privileged static size_t kformat(char *b, size_t n, const char *fmt,
             ++p;
           }
           for (i = j = 0; !pdot || j < prec; ++j) {
-            if (UNLIKELY(!((intptr_t)s & (PAGESIZE - 1)))) {
+            if (UNLIKELY(!((intptr_t)s & 4095))) {
               if (!dang && kisdangerous(s)) break;
             }
             if (!type) {
@@ -687,7 +687,7 @@ privileged static size_t kformat(char *b, size_t n, const char *fmt,
               s += sizeof(char16_t);
               if (IsHighSurrogate(t)) {
                 if (!pdot || j + 1 < prec) {
-                  if (UNLIKELY(!((intptr_t)s & (PAGESIZE - 1)))) {
+                  if (UNLIKELY(!((intptr_t)s & 4095))) {
                     if (!dang && kisdangerous(s)) break;
                   }
                   u = *(const char16_t *)s;