Don't include SCONST symbols in the symbol table when
NotInSymbolTable is set. This is what the old code (genasmsym)
does.
In fact, SCONST symbol is only emitted by the field tracking
code, and is always NotInSymbolTable. So we should just not
include them at all, or not generate SCONST symbols at all. But
at this late stage I'll just restore the old behavior.