Tests: Add coverage for special characters in include directories

We have tests for special characters in preprocessor definitions and
custom command line arguments.  Add such a test for include directories.
Currently the Makefiles generators do not escape paths in `depend.make`
in all cases, so leave a FIXME comment and skip the test for those.

Issue: #20555

Tests/IncludeDirectories/main.cpp

@@ -3,6 +3,17 @@
 #include "SrcProp.h"
 #include "TarProp.h"
 
+#ifdef INCLUDE_SPECIAL_DIR
+#  include "SpecialDir.h"
+#  ifndef SPECIAL_DIR_H
+#    error "SPECIAL_DIR_H not defined"
+#  endif
+#  include "SpecialSpaceDir.h"
+#  ifndef SPECIAL_SPACE_DIR_H
+#    error "SPECIAL_SPACE_DIR_H not defined"
+#  endif
+#endif
+
 int main(int argc, char** argv)
 {
   return 0;