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

third_party/dlmalloc/dlmalloc.c

@@ -1327,20 +1327,6 @@ void dlmalloc_atfork(void) {
 }
 #endif
 
-void* dlvalloc(size_t bytes) {
-  size_t pagesz;
-  ensure_initialization();
-  pagesz = mparams.page_size;
-  return dlmemalign(pagesz, bytes);
-}
-
-void* dlpvalloc(size_t bytes) {
-  size_t pagesz;
-  ensure_initialization();
-  pagesz = mparams.page_size;
-  return dlmemalign(pagesz, (bytes + pagesz - SIZE_T_ONE) & ~(pagesz - SIZE_T_ONE));
-}
-
 void** dlindependent_calloc(size_t n_elements, size_t elem_size,
                             void* chunks[]) {
   size_t sz = elem_size; /* serves as 1-element array */