[configure] simplify checking of zarith

configure.in

@@ -272,34 +272,13 @@ esac
 # zarith
 ########
 
-AC_ARG_ENABLE(
-  zarith,
-  [  --enable-zarith=<dir> use ZArith library],
-  ZARITH_PATH=$enableval,)
-
-AC_MSG_CHECKING(for Zarith)
-
-if test -z "$ZARITH_PATH"; then
-  # standard installation procedure of zarith diverges according to
-  # ocamlfind installation (see zarith's README)
-    ZARITH_PATH=$($OCAMLFIND query zarith 2>/dev/null | tr -d '\r\n')
-    if test -z "$ZARITH_PATH"; then
-      HAS_ZARITH="no";
-    else
-      HAS_ZARITH="yes";
-    fi;
-  if test "$HAS_ZARITH" = "no"; then
-    AC_MSG_ERROR(Zarith not found but required by Frama-C)
-  else
-    AC_MSG_RESULT(found)
-  fi
+AC_MSG_CHECKING(for zarith)
+
+ZARITH=$($OCAMLFIND query zarith -format %v)
+if test -z "$ZARITH" ; then
+  AC_MSG_ERROR(Cannot find zarith via ocamlfind.)
 else
-  AC_CHECK_FILE($ZARITH_PATH/zarith.$LIB_SUFFIX,HAS_ZARITH=yes,HAS_ZARITH=no)
-  if test "$HAS_ZARITH" = "no"; then
-    AC_MSG_ERROR(Zarith: file $ZARITH_PATH/zarith.$LIB_SUFFIX not found.)
-  else
-    AC_MSG_RESULT(found)
-  fi
+  AC_MSG_RESULT(found)
 fi
 
 # apron