Cannot use |= to paddle_error

[Xreki]

We use |= to paddle_error in our benchmark.

Mobile/benchmark/tool/C/inference.cc

Lines 21 to 24 in 6b68be7

	inline paddle_error& operator |=(paddle_error& a, paddle_error b) {
	return a =
	static_cast<paddle_error>(static_cast<int>(a) | static_cast<int>(b));
	}

However, the definition of paddle_error is:
https://github.com/PaddlePaddle/Paddle/blob/c8d4efb20eecab5a2edd55ccf923dac78afc6d78/paddle/capi/error.h#L23-L30

typedef enum {
  kPD_NO_ERROR = 0,
  kPD_NULLPTR = 1,
  kPD_OUT_OF_RANGE = 2,
  kPD_PROTOBUF_ERROR = 3,
  kPD_NOT_SUPPORTED = 4,
  kPD_UNDEFINED_ERROR = -1,
} paddle_error;

The different bit of different error may be the same. If we use |= to two variables of paddle_error, we may lose the error information.

Also, we need to print the error information, or it will be difficult for users to debug, like in #48 .