Move creation of NoDartCoverage file.

Do it after populating the CMake_TestDir variable.
Merge topic 'alt-test-generator' into next

29a5096a Move creation of NoDartCoverage file.
Tests: Build alt-test-generator tests in a separate binary dir.

This way, a single CMake build tree can be used to run the
unit tests with multiple generators.

Move creation of NoDartCoverage file to after populating the
CMake_TestDir variable.
Merge topic 'alt-test-generator' into next

f145e3ba Tests: Build alt-test-generator tests in a separate binary dir.