i965: Enable ARB_gpu_shader_int64 on Gen8+

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/drivers/dri/i965/brw_link.cpp

@@ -120,6 +120,11 @@ process_glsl_ir(struct brw_context *brw,
    }
 
    lower_instructions(shader->ir, instructions_to_lower);
+   lower_64bit_integer_instructions(shader->ir,
+                                    MUL64 |
+                                    DIV64 |
+                                    MOD64 |
+                                    SIGN64);
 
    /* Pre-gen6 HW can only nest if-statements 16 deep.  Beyond this,
     * if-statements need to be flattened.

src/mesa/drivers/dri/i965/intel_extensions.c

@@ -264,6 +264,7 @@ intelInitExtensions(struct gl_context *ctx)
    }
 
    if (brw->gen >= 8) {
+      ctx->Extensions.ARB_gpu_shader_int64 = true;
       ctx->Extensions.ARB_ES3_2_compatibility = true;
    }