dri: Introduce internal Mesa DRI driver loader extension.

All DRI loaders in Mesa (EGL, GLX, gbm) now require this ext and that the
driver come from a matching build.  This will let us use Mesa-internal
types and enums across the loader-driver bounary inside of Mesa.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Acked-by: Eric Engestrom <eric@igalia.com>
LOL-YESed-by: Kristian Høgsberg <krh@bitplanet.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20069>

include/GL/internal/mesa_interface.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright © 2022 Google LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef MESA_INTERFACE_H
+#define MESA_INTERFACE_H
+
+#include "dri_interface.h"
+
+/* Mesa-internal interface between the GLX, GBM, and EGL DRI driver loaders, and
+ * the gallium dri_util.c code.
+ */
+
+typedef struct __DRImesaCoreExtensionRec __DRImesaCoreExtension;
+
+#define __DRI_MESA "DRI_Mesa"
+#define __DRI_MESA_VERSION 1
+
+/**  Core struct that appears alongside __DRI_CORE for Mesa-internal usage.
+ * Implemented in the top-level dri/drisw/kopper extension list.
+ */
+struct __DRImesaCoreExtensionRec {
+   __DRIextension base;
+
+   /* Version string for verifying that the DRI driver is from the same build as
+    * the loader.
+    */
+#define MESA_INTERFACE_VERSION_STRING PACKAGE_VERSION MESA_GIT_SHA1
+   const char *version_string;
+};
+
+#endif /* MESA_INTERFACE_H */