drbd: split off drbd_buildtag into separate file

To be more similar to what we do in the out-of-tree module and ease the
upstreaming process.

Signed-off-by: Christoph Böhmwalder <[e-mail]>
Reviewed-by: Joel Colledge <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/drbd/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-drbd-y := drbd_bitmap.o drbd_proc.o
+drbd-y := drbd_buildtag.o drbd_bitmap.o drbd_proc.o
 drbd-y += drbd_worker.o drbd_receiver.o drbd_req.o drbd_actlog.o
 drbd-y += drbd_main.o drbd_strings.o drbd_nl.o
 drbd-y += drbd_interval.o drbd_state.o

drivers/block/drbd/drbd_buildtag.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/drbd.h>
+#include <linux/module.h>
+
+const char *drbd_buildtag(void)
+{
+	/* DRBD built from external sources has here a reference to the
+	 * git hash of the source code.
+	 */
+
+	static char buildtag[38] = "\0uilt-in";
+
+	if (buildtag[0] == 0) {
+#ifdef MODULE
+		sprintf(buildtag, "srcversion: %-24s", THIS_MODULE->srcversion);
+#else
+		buildtag[0] = 'b';
+#endif
+	}
+
+	return buildtag;
+}

drivers/block/drbd/drbd_main.c

···
 }
 #endif
 
-const char *drbd_buildtag(void)
-{
-	/* DRBD built from external sources has here a reference to the
-	   git hash of the source code. */
-
-	static char buildtag[38] = "\0uilt-in";
-
-	if (buildtag[0] == 0) {
-#ifdef MODULE
-		sprintf(buildtag, "srcversion: %-24s", THIS_MODULE->srcversion);
-#else
-		buildtag[0] = 'b';
-#endif
-	}
-
-	return buildtag;
-}
-
 module_init(drbd_init)
 module_exit(drbd_cleanup)