dfflibmap: add regression test for resetval clobber

tests/techmap/dfflibmap_resetval_clobber.lib

@@ -0,0 +1,52 @@
+library(test) {
+  cell (bad_dff) {
+    area : 1;
+    ff("IQ", "IQN") {
+      next_state : "!D"; // Look here
+      clocked_on : "CLK";
+      preset     : "!RST"; // Look here
+    }
+    pin(D) {
+      direction : input;
+    }
+    pin(CLK) {
+      direction : input;
+    }
+    pin(RST) {
+      direction : input;
+    }
+    pin(Q) {
+      direction: output;
+      function : "IQ";
+    }
+    pin(QN) {
+      direction: output;
+      function : "IQN";
+    }
+  }
+  cell (good_dff) {
+    area : 1;
+    ff("IQ", "IQN") {
+      next_state : "D"; // Look here
+      clocked_on : "CLK";
+      clear      : "RST"; // Look here
+    }
+    pin(D) {
+      direction : input;
+    }
+    pin(CLK) {
+      direction : input;
+    }
+    pin(RST) {
+      direction : input;
+    }
+    pin(Q) {
+      direction: output;
+      function : "IQ";
+    }
+    pin(QN) {
+      direction: output;
+      function : "IQN";
+    }
+  }
+}

tests/techmap/dfflibmap_resetval_clobber.ys

@@ -0,0 +1,13 @@
+read_verilog -icells <<EOT
+module top(input C, D, R, output Q);
+$_DFF_PP0_ ff (.C(C), .D(D), .R(R), .Q(Q));
+endmodule
+EOT
+
+dfflibmap -liberty dfflibmap_resetval_clobber.lib top
+read_liberty dfflibmap_resetval_clobber.lib
+flatten -noscopeinfo
+opt_clean
+
+select -assert-count 1 t:* top %i
+select -assert-count 1 t:$_DFF_PP0_ top %i