Update mercury_error.h
Update mercury_error.h

Users of Mercury that turn warnings to errors and use -Wall can't compile if verbose errors are disabled.  This fixes that by consuming the arguments in the macro.  The (void)0 allows a compiler to catch errors like this

if (...)
    HG_LOG_ERROR("Error Message") //missing semicolon
do_something_important();

mercury-hpc/mercury,mercury-hpc/mercury,mercury-hpc/mercury,mercury-hpc/mercury