[cmake,bugfix] Do use a version when there is not version in the depends or

Previously, we used >=0.0. if there was no version information in the
dependes and suggests clause of a dune.module file. This breaks with
the new more strict version checking. Therefore with this revision no
version gets set if it does not appear in dune.module

cmake/modules/DuneMacros.cmake

@@ -229,7 +229,7 @@ macro(split_module_version STRING MODULES VERSIONS)
       string(REGEX REPLACE "^\\([ ]*([^ ]*[ ]*[^ ]+)[ ]*\\)$" "\\1"
         version ${have_version})
       else(have_version)
-        set(version >=0.0)
+        set(version "")
       endif(have_version)
     list(APPEND ${MODULES} ${mod})
     list(APPEND ${VERSIONS} ${version})