syscall: use fcntl64 on 32-bit GNU/Linux systems

Use fcntl64Syscall in forkAndExecInChild1 to get fcntl64 on 32-bit Linux
systems.

Updates #36211

Change-Id: Id0e34359256beace970e72102fdace7a987ff2b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/212598
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/exec_linux.go

@@ -438,7 +438,7 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 		if err1 != 0 {
 			goto childerror
 		}
-		RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+		RawSyscall(fcntl64Syscall, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
 		pipe = nextfd
 		nextfd++
 	}
@@ -451,7 +451,7 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 			if err1 != 0 {
 				goto childerror
 			}
-			RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+			RawSyscall(fcntl64Syscall, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
 			fd[i] = nextfd
 			nextfd++
 		}
@@ -466,7 +466,7 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 		if fd[i] == int(i) {
 			// dup2(i, i) won't clear close-on-exec flag on Linux,
 			// probably not elsewhere either.
-			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), F_SETFD, 0)
+			_, _, err1 = RawSyscall(fcntl64Syscall, uintptr(fd[i]), F_SETFD, 0)
 			if err1 != 0 {
 				goto childerror
 			}