#1242 Fix for pr3534333

[Martin Whitaker]

The parser has previously been changed to support null statements in sequential and parallel blocks (a feature introduced in SystemVerilog), but this was not supported in elaboration, leading to a compiler crash. This patch fixes this by discarding the null statements during parsing.

An alternative fix would be to discard the null statements during elaboration, but this would require more widespread changes, and for performance reasons it seems better to discard the null statements as early as possible in the compilation process.

Also attached is a regression test to add to the test suite. This test doesn;t need any special compiler flags or a gold file.

This bug is only present in devel.

[Martin Whitaker]

Proposed patch for compiler

[Martin Whitaker]

Regression test for test suite

[Stephen Williams]

Also added regression test to ivtest master.

[Stephen Williams]

Applied to git master.