Prepare a test to find an installed libspdlog

The example should be able to build as a standalone project too if
external libfmt was used.

Require the minimum fmt version with find_package().

TODO: Require the minimum spdlog version with find_package() at
standalone example.

CMakeLists.txt

@@ -149,7 +149,7 @@ target_link_libraries(spdlog_header_only INTERFACE Threads::Threads)
 #---------------------------------------------------------------------------------------
 if(SPDLOG_FMT_EXTERNAL OR SPDLOG_FMT_EXTERNAL_HO)
     if(NOT TARGET fmt::fmt)
-        find_package(fmt REQUIRED)
+        find_package(fmt 6.1.2 REQUIRED)
     endif()
     target_compile_definitions(spdlog PUBLIC SPDLOG_FMT_EXTERNAL)
     target_compile_definitions(spdlog_header_only INTERFACE SPDLOG_FMT_EXTERNAL)
@@ -181,7 +181,6 @@ if(SPDLOG_WCHAR_SUPPORT)
 
 if(SPDLOG_NO_EXCEPTIONS)
     target_compile_definitions(spdlog PUBLIC SPDLOG_NO_EXCEPTIONS)
-
     target_compile_definitions(spdlog_header_only INTERFACE SPDLOG_NO_EXCEPTIONS)
 
     if(NOT MSVC)
@@ -276,8 +275,9 @@ if (SPDLOG_INSTALL)
             FILE ${config_targets_file})
 
     include(CMakePackageConfigHelpers)
-    configure_file("${project_config_in}" "${project_config_out}" @ONLY)
-
+    configure_package_config_file("${project_config_in}" "${project_config_out}"
+        INSTALL_DESTINATION ${export_dest_dir}
+    )
     write_basic_package_version_file("${version_config_file}" COMPATIBILITY SameMajorVersion)
     install(FILES
             "${project_config_out}"

example/CMakeLists.txt

@@ -1,14 +1,19 @@
 # Copyright(c) 2019 spdlog authors
 # Distributed under the MIT License (http://opensource.org/licenses/MIT)
 
-cmake_minimum_required(VERSION 3.1)
-project(spdlog_examples CXX)
+cmake_minimum_required(VERSION 3.2)
 
-include(../cmake/utils.cmake)
+project(spdlog_examples CXX)
 
 if(NOT TARGET spdlog)
     # Stand-alone build
-    find_package(spdlog REQUIRED)
+    set(CMAKE_CXX_STANDARD 11)
+    set(CMAKE_CXX_STANDARD_REQUIRED ON)
+    #XXX MAYBE: include(../cmake/clang-tidy.cmake)
+    include(../cmake/utils.cmake)
+    #TODO spdlog_extract_version()
+
+    find_package(spdlog ${SPDLOG_VERSION} REQUIRED)
 endif()
 
 #---------------------------------------------------------------------------------------