Add test for writing gzip-compressed files

Signed-off-by: David Shah <dave@ds0.me>

tests/various/.gitignore

@@ -1,2 +1,4 @@
 /*.log
 /*.out
+/write_gzip.v
+/write_gzip.v.gz

tests/various/write_gzip.ys

@@ -0,0 +1,16 @@
+read -vlog2k <<EOT
+module top(input a, output y);
+assign y = !a;
+endmodule
+EOT
+
+prep -top top
+write_verilog write_gzip.v.gz
+design -reset
+
+! rm -f write_gzip.v
+! gunzip write_gzip.v.gz
+read -vlog2k write_gzip.v
+! rm -f write_gzip.v
+hierarchy -top top
+select -assert-any top