KNOWNBUG test for SVA sequence concatenation

This adds a KNOWNBUG test for the SVA sequence concatenation operator.

Author: kroening

regression/verilog/SVA/sequence4.desc

@@ -0,0 +1,9 @@
+KNOWNBUG
+sequence4.sv
+--bound 10
+^EXIT=10$
+^SIGNAL=0$
+--
+^warning: ignoring
+--
+sequence concatenation is not supported by the BMC engine

regression/verilog/SVA/sequence4.sv

@@ -0,0 +1,14 @@
+module main;
+
+  reg [31:0] x;
+  wire clk;
+
+  initial x=0;
+
+  always @(posedge clk)
+    x<=x+1;
+
+  // sequence concatenation
+  initial p0: assert property (x == 0 ##1 x == 1 ##1 x == 2);
+
+endmodule