add new Literal API for pure literal expressions:

Design compile time api hs_compile_lit() and hs_compile_lit_multi()
to handle pure literal pattern sets. Corresponding option --literal-on
is added for hyperscan testing suites. Extended parameters and part of
flags are not supported for this api.

src/fdr/fdr_compile.cpp

@@ -807,9 +807,6 @@ void findIncludedLits(vector<hwlmLiteral> &lits,
         for (size_t i = 0; i < cnt; i++) {
             u32 bucket1 = group[i].first;
             u32 id1 = group[i].second;
-            if (lits[id1].pure) {
-                continue;
-            }
             buildSquashMask(lits, id1, bucket1, i + 1, group, parent_map,
                             exception_map);
         }