Allow assert disable (#2168)

* Add +verilator+noassert flag

This allows to disable the assert check per simulation argument.

* Add AssertOn check for assert

Insert the check AssertOn to allow disabling of asserts.
Asserts can be disabled by not using the `--assert` flag or by calling
`AssertOn(false)`, or passing the "+verilator+noassert" runtime flag.
Add tests for this behavior.
Bad tests check that the assert still causes a stop.
Non bad tests check that asserts are properly disabled and cause no stop
of the simulation.

Fixes #2162.

Signed-off-by: Tobias Wölfel <[email protected]>

* Correct file location

Signed-off-by: Tobias Wölfel <[email protected]>

* Add description for single test execution

Without this description it is not obvious how to run a single test from
the regression test suite.

Signed-off-by: Tobias Wölfel <[email protected]>

src/V3Assert.cpp

@@ -150,7 +150,7 @@ private:
             // It's more LIKELY that we'll take the NULL if clause
             // than the sim-killing else clause:
             ifp->branchPred(VBranchPred::BP_LIKELY);
-            bodysp = ifp;
+            bodysp = newIfAssertOn(ifp);
         } else {
             nodep->v3fatalSrc("Unknown node type");
         }