Avoid storing "_version-NOTFOUND" in ELF metadata.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit 184d1c2a4d)

modules/TDEMacros.cmake

@@ -922,6 +922,7 @@ macro( tde_add_library _arg_target )
       else( )
         set( _location "${_destination}/${_output}" )
         set( _soname "${_output}" )
+        unset( _version )
       endif( )
 
       configure_file( ${CMAKE_SOURCE_DIR}/cmake/modules/template_export_library.cmake "${PROJECT_BINARY_DIR}/export-${_target}.cmake" @ONLY )