glsl: Enable AMD_conservative_depth in parser

All the necessary compiler infrastructure for AMD_conservative_depth is in
place, so it's safe to enable it in the parser.

src/glsl/glsl_parser_extras.cpp

@@ -219,6 +219,13 @@ _mesa_glsl_process_extension(const char *name, YYLTYPE *name_locp,
 	 state->ARB_shader_stencil_export_warn = (ext_mode == extension_warn);
 	 unsupported = !state->extensions->ARB_shader_stencil_export;
       }
+   } else if (strcmp(name, "GL_AMD_conservative_depth") == 0) {
+      /* The AMD_conservative spec does not forbid requiring the extension in
+       * the vertex shader.
+       */
+      state->AMD_conservative_depth_enable = (ext_mode != extension_disable);
+      state->AMD_conservative_depth_warn = (ext_mode == extension_warn);
+      unsupported = !state->extensions->AMD_conservative_depth;
    } else {
       unsupported = true;
    }