Specify CXX language explicitly in CMake

Marking project as CXX will disable detecting C compiler and other checks.
Removed 'INCLUDES DESTINATION' as it made the include path appear doubled.

CMakeLists.txt

@@ -4,7 +4,7 @@
 #
 
 cmake_minimum_required(VERSION 3.1)
-project(spdlog VERSION 0.16.3)
+project(spdlog VERSION 0.16.3 LANGUAGES CXX)
 include(CTest)
 include(CMakeDependentOption)
 include(GNUInstallDirs)
@@ -73,7 +73,6 @@ configure_file("cmake/spdlog.pc.in" "${pkg_config}" @ONLY)
 install(
     TARGETS spdlog
     EXPORT "${targets_export_name}"
-    INCLUDES DESTINATION "${include_install_dir}"
 )
 
 # install headers

example/CMakeLists.txt

@@ -22,7 +22,7 @@
 # *************************************************************************/
 
 cmake_minimum_required(VERSION 3.0)
-project(SpdlogExamples)
+project(SpdlogExamples CXX)
 
 if(TARGET spdlog)
   # Part of the main project

tests/CMakeLists.txt

-project(spdlog-utests)
+project(spdlog-utests CXX)
 
 enable_testing()
 find_package(Threads REQUIRED)