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

test/libc/sock/nonblock_test.c

@@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
 #include "libc/errno.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/runtime/runtime.h"
 #include "libc/runtime/syslib.internal.h"
@@ -106,8 +107,9 @@ TEST(O_NONBLOCK, canBeTunedWithFcntl_toMakeReadNonBlocking) {
   PARENT();
   EXPECT_SYS(0, 0, close(3));
   ASSERT_SYS(0, 3, socket(AF_INET, SOCK_STREAM, IPPROTO_TCP));
+  ASSERT_SYS(0, O_RDWR, fcntl(3, F_GETFL));
   ASSERT_SYS(0, 0, connect(3, (struct sockaddr *)&addr, sizeof(addr)));
-  ASSERT_SYS(0, 0, fcntl(3, F_SETFL, O_NONBLOCK));
+  ASSERT_SYS(0, 0, fcntl(3, F_SETFL, O_RDWR | O_NONBLOCK));
   ASSERT_SYS(EAGAIN, -1, read(3, buf, 16));
   EXPECT_EQ(0, pthread_spin_unlock(phaser + 0));
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