Added initial tests for --glsl-version

- Added compilation tests for shader stages using a different
  version at each stage.

Test/glsl.versionOverride.frag

@@ -0,0 +1,11 @@
+/*
+
+glslangValidator.exe --glsl-version 420 -V -S frag -o glsl.versionOverride.frag.out glsl.versionOverride.frag
+
+*/
+
+#version 330
+
+void main()
+{
+}