Mark pattern labels as unremoveable

Peephole optimization doesn't play well with find pattern at
least. The only case when a pattern matching could have
unreachable patterns is when we have lasgn/dasgn node, which
shouldn't happen in real-life.

Fixes https://bugs.ruby-lang.org/issues/17534

compile.c

@@ -6408,11 +6408,11 @@ compile_case3(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
             int pat_line = nd_line(pattern);
             LABEL *next_pat = NEW_LABEL(pat_line);
             ADD_INSN (cond_seq, pat_line, dup);
-
             // NOTE: set deconstructed_pos to the current cached value location
             // (it's "under" the matchee value, so it's position is 2)
             CHECK(iseq_compile_pattern_each(iseq, cond_seq, pattern, l1, next_pat, FALSE, 2));
             ADD_LABEL(cond_seq, next_pat);
+            LABEL_UNREMOVABLE(next_pat);
         }
         else {
             COMPILE_ERROR(ERROR_ARGS "unexpected node");

test/ruby/test_pattern_matching.rb

@@ -791,6 +791,16 @@ END
         true
       end
     end
+
+    # https://bugs.ruby-lang.org/issues/17534
+    assert_block do
+      case [0, 1, 2]
+      in x
+        true
+      in [*, 2, *]
+        false
+      end
+    end
   end
 
   def test_hash_pattern