main: Allow compute shaders to be compiled with OpenGLES 3.1

Previous OpenGLES 3.1 testing had been done when ARB_compute_shader
was overridden to enabled.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Marta Lofstedt <marta.lofstedt@intel.com>

src/mesa/main/shaderapi.c

@@ -208,7 +208,7 @@ _mesa_validate_shader_target(const struct gl_context *ctx, GLenum type)
    case GL_TESS_EVALUATION_SHADER:
       return ctx == NULL || _mesa_has_tessellation(ctx);
    case GL_COMPUTE_SHADER:
-      return ctx == NULL || ctx->Extensions.ARB_compute_shader;
+      return ctx == NULL || _mesa_has_compute_shaders(ctx);
    default:
       return false;
    }