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/mem/free.c

@@ -27,9 +27,7 @@ void (*hook_free)(void *) = dlfree;
  *
  * Releases the chunk of memory pointed to by p, that had been
  * previously allocated using malloc or a related routine such as
- * realloc. It has no effect if p is null. If p was not malloced or
- * already freed, free(p) will by default cause the current program to
- * abort.
+ * realloc. It has no effect if p is null.
  *
  * @param p is allocation address, which may be NULL
  * @see dlfree()