This error was originally added a while(7 years) ago when
including multiple files was basically always an error. Tablegen
now has preprocessor support, which allows for building nice
c/c++ style include guards. With the current error being
reported, we unfortunately need to double guard when including
files:
* In user of MyFile.td
#ifndef MYFILE_TD
include MyFile.td
#endif
* In MyFile.td
#ifndef MYFILE_TD
#define MYFILE_TD
...
#endif
Differential Revision: https://reviews.llvm.org/D70410
