The cmake/spdlogConfig.cmake.in file properly takes into account the fmt
package dependency when building with SPDLOG_FMT_EXTERNAL:BOOL=ON but
not when built with SPDLOG_FMT_EXTERNAL_HO:BOOL=ON.
Prior to these changes SPDLOG_FMT_EXTERNAL_HO:BOOL=ON results in
exported targets with INTERFACE_LINK_LIBRARIES that contain
fmt::fmt-header-only.
As such, the installed spdlogConfig.cmake file should attempt to find
that dependency for the consumer.
69cac816aa