Update configure.ac with some m4 magic to add a git commit id

 and a reference of the last tag, the changes since then and the
 dirty flag from `git describe`

configure.ac

@@ -1,12 +1,20 @@
 #                                               -*- Autoconf -*-
 # Process this file with autoconf to produce a configure script.
 
+# ----------------------------------------------------------------------
+# Build version string.
+# ----------------------------------------------------------------------
+
+m4_define([htop_git_version],
+  m4_normalize(m4_esyscmd([git describe --abbrev=7 --dirty --always --tags 2> /dev/null || echo ''])))
+m4_define([htop_release_version], [3.4.0-dev])
+
 # ----------------------------------------------------------------------
 # Autoconf initialization.
 # ----------------------------------------------------------------------
 
 AC_PREREQ([2.69])
-AC_INIT([htop], [3.4.0-dev], [[email protected]], [], [https://htop.dev/])
+AC_INIT([htop], [m4_join([-],m4_defn([htop_release_version]),m4_defn([htop_git_version]))], [[email protected]], [], [https://htop.dev/])
 
 AC_CONFIG_SRCDIR([htop.c])
 AC_CONFIG_AUX_DIR([build-aux])