message: Fix build for ubunu xenial
diff: # /usr/bin/x86_64-linux-gnu-ld: /usr/lib/gcc/x86_64-linux-gnu/8/../../../x86_64-linux-gnu/libltdl.a(libltdl_libltdl_la-lt__alloc.o): relocation R_X86_64_PC32 against symbol `stderr@@GLIBC_2.2.5' can not be used when making a shared object; recompile with -fPIC
  if (NOT BUILD_SHARED)
  execute_process(COMMAND lsb_release -cs OUTPUT_VARIABLE _codename OUTPUT_STRIP_TRAILING_WHITESPACE)
  - if (_codename STREQUAL "bionic" OR _codename STREQUAL "trusty")
  + if (_codename STREQUAL "bionic" OR _codename STREQUAL "xenial" OR _codename STREQUAL "trusty")
  list (REVERSE CMAKE_FIND_LIBRARY_SUFFIXES)
  set (_suffixes_reversed 1)
  message (STATUS "Trying to find shared version of ltdl library because linking with libltdl.a is broken in ${_codename}")
  