internal: add poll() method

Add the poll() method to the internal syscall interface.

Change-Id: I6bf8b59e582214c7e607a8041a9573ef24dd5493
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/internal_sys_mock.hpp b/test/internal_sys_mock.hpp
index 2210d6f..8424723 100644
--- a/test/internal_sys_mock.hpp
+++ b/test/internal_sys_mock.hpp
@@ -20,6 +20,7 @@
     MOCK_CONST_METHOD2(munmap, int(void*, size_t));
     MOCK_CONST_METHOD0(getpagesize, int());
     MOCK_CONST_METHOD3(ioctl, int(int, unsigned long, void*));
+    MOCK_CONST_METHOD3(poll, int(struct pollfd*, nfds_t, int));
 };
 
 } // namespace internal