* [spdlog]Upgrade version to 1.4.2
* [spdlog]Do not remove these libraries.
* [spdlog]Fix error C4275 when use fmt.
* [spdlog]Re-fix C4275 error.
* [spdlog]Re-fix C4275 error.
* [spdlog]Disable build on uwp.
* [spdlog]Fix build with uwp.
Using an external fmt lib should cause the spdlog::spdlog target to have
a dependency on fmt lib - so that a consuming project does not need
to call find_package(fmt) and target_link_libraries(... fmt::fmt).
To this end a new cmake option SPDLOG_FMT_EXTERNAL is introduced which
makes spdlog depend on fmt lib and defines the SPDLOG_FMT_EXTERNAL macro
to avoid using the bundled fmt lib. The value of SPDLOG_FMT_EXTERNAL is
also stored in the installed spdlogConfig.cmake and if it is ON
find_dependency() is used to ensure the fmt::fmt target is imported.
