cl21: Add minimal required version functionality (#270)

This adds functionality to define minimal required version through the
ADD_TEST* macros. Tests that don't meet the version requirement will
be skipped.

By default the minimal required version is set to 1.0, subsequent
patches will set the appropriate version for each of the tests.

Signed-off-by: Radek Szymanski <radek.szymanski@arm.com>

test_conformance/spirv_new/main.cpp

@@ -79,6 +79,7 @@ void spirvTestsRegistry::addTestClass(baseTestClass *test, const char *testName)
     test_definition testDef;
     testDef.func = test->getFunction();
     testDef.name = testName;
+    testDef.min_version = Version(2, 1);
     testDefinitions.push_back(testDef);
 }