We were checking HAVE_COGL_GLES2 but this is not publicly defined by
Cogl so since splitting Cogl from Clutter test-cogl-materials.c would
not have built against gles2 since it would end up enabling the GL
specific code path which would reference an undefined symbol.
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>