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.h

@@ -98,13 +98,6 @@ void* dlmemalign(size_t, size_t);
 */
 int dlposix_memalign(void**, size_t, size_t);
 
-/*
-  valloc(size_t n);
-  Equivalent to memalign(pagesize, n), where pagesize is the page
-  size of the system. If the pagesize is unknown, 4096 is used.
-*/
-void* dlvalloc(size_t);
-
 /*
   mallopt(int parameter_number, int parameter_value)
   Sets tunable parameters The format is to provide a
@@ -348,13 +341,6 @@ void** dlindependent_comalloc(size_t, size_t*, void**);
 */
 size_t dlbulk_free(void**, size_t n_elements);
 
-/*
-  pvalloc(size_t n);
-  Equivalent to valloc(minimum-page-that-holds(n)), that is,
-  round up n to nearest pagesize.
- */
-void* dlpvalloc(size_t);
-
 /*
   malloc_trim(size_t pad);