Generate runtime conversion diagnostics

Instead of inserting a comment with error description into the generated code,
generate a call to a function that will print out a conversion error when executed.
Do not print generic "partially converted" message anymore.
Remove --verbose and --no_warnings options.

Bug: 204062171
Test: internal
Change-Id: Ib126e16dc76f49635e4939e670922f2561781049

mk2rbc/variable.go

@@ -228,10 +228,9 @@ func (pv predefinedVariable) emitSet(gctx *generationContext, asgn *assignmentNo
 			if actualValue == expectedValue {
 				return
 			}
-			gctx.writef("# MK2RBC TRANSLATION ERROR: cannot set predefined variable %s to %q, its value should be %q",
-				pv.name(), actualValue, expectedValue)
-			gctx.newLine()
-			gctx.write("pass")
+			gctx.emitConversionError(asgn.location,
+				fmt.Sprintf("cannot set predefined variable %s to %q, its value should be %q",
+					pv.name(), actualValue, expectedValue))
 			gctx.starScript.hasErrors = true
 			return
 		}