vrend: Add extensions that enable barriers on OpenGL < 4.2

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>

src/vrend_renderer.c

@@ -225,7 +225,7 @@ static const  struct {
    FEAT(ati_meminfo, UNAVAIL, UNAVAIL, "GL_ATI_meminfo" ),
    FEAT(atomic_counters, 42, 31,  "GL_ARB_shader_atomic_counters" ),
    FEAT(base_instance, 42, UNAVAIL,  "GL_ARB_base_instance", "GL_EXT_base_instance" ),
-   FEAT(barrier, 42, 31, NULL),
+   FEAT(barrier, 42, 31, "GL_ARB_shader_image_load_store"),
    FEAT(bind_vertex_buffers, 44, UNAVAIL, NULL),
    FEAT(bit_encoding, 33, UNAVAIL,  "GL_ARB_shader_bit_encoding" ),
    FEAT(blend_equation_advanced, UNAVAIL, 32,  "GL_KHR_blend_equation_advanced" ),
@@ -281,7 +281,7 @@ static const  struct {
    FEAT(separate_shader_objects, 41, 31, "GL_ARB_seperate_shader_objects"),
    FEAT(shader_clock, UNAVAIL, UNAVAIL,  "GL_ARB_shader_clock" ),
    FEAT(ssbo, 43, 31,  "GL_ARB_shader_storage_buffer_object" ),
-   FEAT(ssbo_barrier, 43, 31, NULL),
+   FEAT(ssbo_barrier, 43, 31, "GL_ARB_shader_storage_buffer_object"),
    FEAT(srgb_write_control, 30, UNAVAIL, "GL_EXT_sRGB_write_control"),
    FEAT(stencil_texturing, 43, 31,  "GL_ARB_stencil_texturing" ),
    FEAT(storage_multisample, 43, 31,  "GL_ARB_texture_storage_multisample" ),