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

tool/build/runitd.c

@@ -105,9 +105,9 @@
 bool use_ftrace;
 bool use_strace;
 char *g_exepath;
+unsigned char g_buf[4096];
 volatile bool g_interrupted;
 struct sockaddr_in g_servaddr;
-unsigned char g_buf[PAGESIZE];
 bool g_daemonize, g_sendready;
 int g_timeout, g_bogusfd, g_servfd, g_clifd, g_exefd;