techmap: Fix cell names with _TECHMAP_REPLACE_.*

Fixes #1804.

tests/techmap/techmap_replace.ys

@@ -16,3 +16,21 @@ EOT
 techmap -map %techmap
 select -assert-any w:s0.asdf
 select -assert-any c:s0.blah
+
+read_verilog <<EOT
+module sub(input i, output o, input j);
+wire _TECHMAP_REPLACE_.asdf = i ;
+barfoo _TECHMAP_REPLACE_.blah (i, o, j);
+endmodule
+EOT
+design -stash techmap
+
+read_verilog <<EOT
+module top(input i, output o);
+sub s0(i, o);
+endmodule
+EOT
+
+techmap -map %techmap
+select -assert-any w:s0.asdf
+select -assert-any c:s0.blah