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/runtime/memtrack.internal.h

@@ -141,10 +141,6 @@ forceinline pureconst bool IsShadowFrame(int x) {
   return 0x7fff <= x && x < 0x10008000;
 }
 
-forceinline pureconst bool IsArenaFrame(int x) {
-  return 0x5004 <= x && x <= 0x7ffb;
-}
-
 forceinline pureconst bool IsStaticStackFrame(int x) {
   intptr_t stack = GetStaticStackAddr(0);
   return (int)(stack >> 16) <= x &&
@@ -192,19 +188,6 @@ forceinline pureconst bool OverlapsImageSpace(const void *p, size_t n) {
   }
 }
 
-forceinline pureconst bool OverlapsArenaSpace(const void *p, size_t n) {
-  intptr_t BegA, EndA, BegB, EndB;
-  if (n) {
-    BegA = (intptr_t)p;
-    EndA = BegA + (n - 1);
-    BegB = 0x50000000;
-    EndB = 0x7ffdffff;
-    return MAX(BegA, BegB) < MIN(EndA, EndB);
-  } else {
-    return 0;
-  }
-}
-
 forceinline pureconst bool OverlapsShadowSpace(const void *p, size_t n) {
   intptr_t BegA, EndA, BegB, EndB;
   if (n) {