ENH: create new test to test subdir exclude

Tests/SubDir/Examples/example1/CMakeLists.txt

@@ -0,0 +1,6 @@
+PROJECT(example1)
+ADD_EXECUTABLE(example1 example1.cxx)
+
+ADD_CUSTOM_COMMAND(TARGET example1 POST_BUILD
+  COMMAND "${CMAKE_COMMAND}" ARGS -E remove ${SUBDIR_BINARY_DIR}/ShouldBeHere
+  COMMENT "Remove marker file that should exist because this should not be run")

Tests/SubDir/Examples/example1/example1.cxx

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main()
+{
+  printf("example1\n");
+  return 0;
+}