Avoid compiler warning in operator_schema.h
Avoid compiler warning in operator_schema.h

Summary:
Previous attempt included terminating the program which is
not good. Here I am using [[noreturn]] trick.

Reviewed By: jamesr66a

Differential Revision: D5313159

fbshipit-source-id: 8889efcf793d44d472502309992e6f5b0a31f0e6

sf-wind/caffe2,xzturn/caffe2,pietern/caffe2,xzturn/caffe2,bwasti/caffe2,davinwang/caffe2,pietern/caffe2,bwasti/caffe2,Yangqing/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,bwasti/caffe2,bwasti/caffe2,Yangqing/caffe2,sf-wind/caffe2,bwasti/caffe2,sf-wind/caffe2,pietern/caffe2,pietern/caffe2,davinwang/caffe2,Yangqing/caffe2,davinwang/caffe2,pietern/caffe2,caffe2/caffe2,sf-wind/caffe2,xzturn/caffe2,sf-wind/caffe2,davinwang/caffe2,Yangqing/caffe2,davinwang/caffe2