SystemVerilog: tests for import errors

This adds tests for various error scenarios importing identifiers from
packages.

Author: kroening

regression/verilog/packages/import6.desc

@@ -0,0 +1,8 @@
+KNOWNBUG
+import6.sv
+--bound 0
+^EXIT=2$
+^SIGNAL=0$
+--
+--
+This should be an error.

regression/verilog/packages/import6.sv

@@ -0,0 +1,11 @@
+package my_pkg;
+  parameter my_parameter = 1;
+endpackage
+
+module main;
+  import my_pkg::my_parameter;
+
+  // this is an error: the identifier is already in the scope
+  parameter my_parameter = 2;
+
+endmodule

regression/verilog/packages/import7.desc

@@ -0,0 +1,7 @@
+CORE
+import7.sv
+--bound 0
+^EXIT=10$
+^SIGNAL=0$
+--
+--

regression/verilog/packages/import7.sv

@@ -0,0 +1,11 @@
+package my_pkg;
+  parameter my_parameter = 1;
+endpackage
+
+module main;
+  import my_pkg::*;
+
+  // this is ok: my_pkg::P is only "potentially locally visible" (1800 2017 26.3)
+  parameter my_parameter = 2;
+
+endmodule

regression/verilog/packages/import8.desc

@@ -0,0 +1,8 @@
+KNOWNBUG
+import8.sv
+--bound 0
+^EXIT=2$
+^SIGNAL=0$
+--
+--
+This should be an error.

regression/verilog/packages/import8.sv

@@ -0,0 +1,15 @@
+package my_pkg;
+  parameter my_parameter = 1;
+endpackage
+
+module main;
+  // This makes my_pkg::my_parameter "potentially locally visible"
+  import my_pkg::*;
+
+  // This makes it "locally visible".
+  parameter Q = my_parameter;
+
+  // This is an error. The above made my_parameter visible in this scope.
+  parameter my_parameter = 2;
+
+endmodule