[Pal/Linux-SGX] Set CLOEXEC on /dev/isgx and /dev/gsgx

On host exec, file descriptors for /dev/isgx and /dev/gsgx are leaked.
Set CLOEXEC for them to be closed when emulating fork/exec by using host
exec.

Pal/src/host/Linux-SGX/sgx_framework.c

@@ -15,17 +15,19 @@ void * zero_page;
 
 int open_gsgx(void)
 {
-    gsgx_device = INLINE_SYSCALL(open, 3, GSGX_FILE, O_RDWR, 0);
+    gsgx_device = INLINE_SYSCALL(open, 3, GSGX_FILE, O_RDWR | O_CLOEXEC, 0);
     if (IS_ERR(gsgx_device)) {
         SGX_DBG(DBG_E, "Cannot open device " GSGX_FILE ". Please make sure the"
                 " \'graphene_sgx\' kernel module is loaded.\n");
         return -ERRNO(gsgx_device);
     }
 
-    isgx_device = INLINE_SYSCALL(open, 3, ISGX_FILE, O_RDWR, 0);
+    isgx_device = INLINE_SYSCALL(open, 3, ISGX_FILE, O_RDWR | O_CLOEXEC, 0);
     if (IS_ERR(isgx_device)) {
         SGX_DBG(DBG_E, "Cannot open device " ISGX_FILE ". Please make sure the"
                 " Intel SGX kernel module is loaded.\n");
+        INLINE_SYSCALL(close, 1, gsgx_device);
+        gsgx_device = -1;
         return -ERRNO(isgx_device);
     }