+ have to extend the bits allocated to the pure ISA number.
+
+ These architecture bits come in two flavors:
+ ISA dependent - marking insns that should be included in the opcode
+ set if that architecture is requested on the gencode command line
+ AND the ISA of the insn is <= requested ISA;
+
+ ISA independent - marking insn that should be included in the opcode
+ set if that architecture is requested
+ OR the ISA of the insn is <= requested ISA.
+
+ Independent bits are listed in MASK_ISA_INDEP, the rest are dependent.
+ */