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.

tests/CMakeLists.txt

@@ -1,23 +1,23 @@
-project(spdlog-utests)
-
-enable_testing()
-find_package(Threads REQUIRED)
-
-set(SPDLOG_UTESTS_SOURCES
-    errors.cpp
-    file_helper.cpp
-    file_log.cpp
-    format.cpp
-    includes.h
-    registry.cpp
-    test_macros.cpp
-    utils.cpp
-    utils.h
-    main.cpp)
-
-add_executable(${PROJECT_NAME} ${SPDLOG_UTESTS_SOURCES})
-target_link_libraries(${PROJECT_NAME} PRIVATE Threads::Threads)
-target_link_libraries(${PROJECT_NAME} PRIVATE spdlog)
-
-add_test(NAME ${PROJECT_NAME} COMMAND ${PROJECT_NAME})
-file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/logs")
+project(spdlog-utests CXX)
+
+enable_testing()
+find_package(Threads REQUIRED)
+
+set(SPDLOG_UTESTS_SOURCES
+    errors.cpp
+    file_helper.cpp
+    file_log.cpp
+    format.cpp
+    includes.h
+    registry.cpp
+    test_macros.cpp
+    utils.cpp
+    utils.h
+    main.cpp)
+
+add_executable(${PROJECT_NAME} ${SPDLOG_UTESTS_SOURCES})
+target_link_libraries(${PROJECT_NAME} PRIVATE Threads::Threads)
+target_link_libraries(${PROJECT_NAME} PRIVATE spdlog)
+
+add_test(NAME ${PROJECT_NAME} COMMAND ${PROJECT_NAME})
+file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/logs")