jni: more O_CLOEXECs

Prevent FDs from leaking across an execve() boundary.

Test: compiles and boots
Change-Id: I5f91046917b55b6abead0a5c6e939f82814e6f18
diff --git a/core/jni/android_hardware_SerialPort.cpp b/core/jni/android_hardware_SerialPort.cpp
index 190ddce..3ff2446 100644
--- a/core/jni/android_hardware_SerialPort.cpp
+++ b/core/jni/android_hardware_SerialPort.cpp
@@ -134,7 +134,7 @@
 
     int fd = jniGetFDFromFileDescriptor(env, fileDescriptor);
     // duplicate the file descriptor, since ParcelFileDescriptor will eventually close its copy
-    fd = dup(fd);
+    fd = fcntl(fd, F_DUPFD_CLOEXEC, 0);
     if (fd < 0) {
         jniThrowException(env, "java/io/IOException", "Could not open serial port");
         return;