fix(version): include codspeed iteration in --version output

Derive v_suffix_ver in configure.ac from the top entry of
debian/changelog so AC_INIT picks up the codspeedN iteration
automatically, and join it with '-' to match the git-tag /
deb-version format.

Before: valgrind-3.26.0.codspeed
After:  valgrind-3.26.0-codspeed2

Author: not-matthias

configure.ac

@@ -19,7 +19,11 @@ m4_define([v_major_ver], [3])
 m4_define([v_minor_ver], [26])
 m4_define([v_micro_ver], [0])
 m4_define([v_suffix_ver], [])
-m4_define([v_suffix_ver], [codspeed])
+m4_define([v_suffix_ver],
+	  m4_esyscmd_s([sed -n '1s/.*-[0-9]*\(codspeed[0-9]*\).*/\1/p' debian/changelog]))
+m4_if(m4_bregexp(v_suffix_ver, [^codspeed[0-9]+$]), [-1],
+      [m4_fatal([invalid codspeed suffix ']v_suffix_ver[' extracted from debian/changelog])])
+
 m4_define([v_rel_date], ["5 Nov 2025"])
 m4_define([v_version],
 	  m4_if(v_suffix_ver, [],