Use git describe for BIRD version

Based on patch from Pavel Tvrdik

Makefile.in

@@ -21,6 +21,11 @@ INSTALL=@INSTALL@
 INSTALL_PROGRAM=@INSTALL_PROGRAM@
 INSTALL_DATA=@INSTALL_DATA@
 
+git-label:=$(strip $(shell git describe --always --dirty=-x 2>/dev/null))
+ifneq ($(git-label),)
+        CFLAGS += -DGIT_LABEL="$(git-label)"
+endif
+
 client=$(addprefix $(exedir)/,@CLIENT@)
 daemon=$(exedir)/bird
 protocols=@protocols@

sysdep/config.h

@@ -6,8 +6,15 @@
 #ifndef _BIRD_CONFIG_H_
 #define _BIRD_CONFIG_H_
 
+#define XSTR2(X) #X
+#define XSTR1(X) XSTR2(X)
+
 /* BIRD version */
+#ifdef GIT_LABEL
+#define BIRD_VERSION XSTR1(GIT_LABEL)
+#else
 #define BIRD_VERSION "2.0.0"
+#endif
 
 /* Include parameters determined by configure script */
 #include "sysdep/autoconf.h"