const2ast: add diagnostics tests

tests/verilog/constparser_f.ys

@@ -0,0 +1,6 @@
+read_verilog <<EOT
+module test (y);
+    output signed [2:0] y = 1'b1;
+endmodule
+EOT
+dump

tests/verilog/constparser_f_file.sv

@@ -0,0 +1,3 @@
+module test (y);
+    output signed [2:0] y = 1'bf;
+endmodule

tests/verilog/constparser_f_file.ys

@@ -0,0 +1,2 @@
+logger -expect prefix-error "./constparser_f_file.sv:2: ERROR: Digit larger than 1 used in in base-2 constant." 1
+read_verilog -sv ./constparser_f_file.sv

tests/verilog/constparser_g.ys

@@ -0,0 +1,6 @@
+logger -expect prefix-error "<<EOT:2: ERROR: syntax error, unexpected invalid token, expecting TOK_BASED_CONSTVAL" 1
+read_verilog <<EOT
+module test (y);
+    output signed [2:0] y = 1'bg;
+endmodule
+EOT