spdlog is linked "public" in BaseLib.

Reason is the violation of odr for some globals defined
in the spdlog library.

==1540297==ERROR: AddressSanitizer: odr-violation (0x7f5ea9c9d020):
  [1] size=40 'vtable for spdlog::spdlog_ex' _deps/spdlog-src/src/spdlog.cpp
  [2] size=40 'vtable for spdlog::spdlog_ex' _deps/spdlog-src/src/spdlog.cpp
These globals were registered at these points:
  [1]:
    #0 0x5614686e0dfa in __asan_register_globals.part.0 (/home/naumov/w/ogs/d/bin/ogs+0x1bfdfa)
    #1 0x7f5e6cdbe7eb in asan.module_ctor (/home/naumov/w/ogs/d/bin/../lib/libMeshLib.so+0x17d37eb)

  [2]:
    #0 0x558bd62b6dfa in __asan_register_globals.part.0 (/home/naumov/w/ogs/d/bin/ogs+0x1bfdfa)
    #1 0x7f831c7e54ab in asan.module_ctor (/home/naumov/w/ogs/d/bin/../lib/libBaseLib.so+0x89a4ab)