[llvm-c] Make LLVMGetStringErrorTypeId a proper prototype

[wanders]

Summary

In C a function declaration with an empty argument list isn't a real
prototype, it will allow calling the function with any number of
arguments. It will also cause warnings when used in C code compiled with
'-Wstrict-prototypes'

llvm/include/llvm-c/Error.h

 /**
  * Dispose of the given error message.
  */
 void LLVMDisposeErrorMessage(char *ErrMsg);
 
 /**
  * Returns the type id for llvm StringError.
  */
-LLVMErrorTypeId LLVMGetStringErrorTypeId();
+LLVMErrorTypeId LLVMGetStringErrorTypeId(void);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif