[wp] Fixes Coq compilation constraints

opam/opam

@@ -132,6 +132,6 @@ depopts: [
 messages: [
   "The Frama-C/Wp now uses Why-3 for all provers (Cf. deprecated -wp-prover native:alt-ergo)"
   {alt-ergo:installed}
-  "The Frama-C/Wp native support for Coq is now deprecated (use TIP or Why-3 instead)."
+  "The Frama-C/Wp native support for Coq is deprecated and only activated with Coq.8.12.x (use TIP or Why-3 instead)."
   {coq:installed}
 ]

src/plugins/wp/configure.ac

@@ -85,16 +85,14 @@ if test "$ENABLE_WP" != "no"; then
     if test "$COQC" = "yes" ; then
       COQVERSION=`coqc -v | sed -n -e 's|.*version* *\([[^ ]]*\) .*$|\1|p' `
       case $COQVERSION in
-        8.7*|8.8*|8.9*|8.10*|8.11.*|8.12.*|trunk)
+        8.12.*|trunk)
           AC_MSG_RESULT(coqc version $COQVERSION found)
           ;;
         *)
-          AC_MSG_RESULT(unsupported coqc version $COQVERSION)
+          AC_MSG_RESULT(unsupported coqc version $COQVERSION for - deprecated - native backend)
           COQC="no"
           ;;
       esac
-    else
-      AC_MSG_NOTICE(rerun configure to make wp using coq 8.7.2 or higher)
     fi
   else
     COQC="no"