add feature detection machinery

detect/features.cmake

@@ -0,0 +1,19 @@
+if(cxx_noexcept IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+    set(RING_BUFFER_NOEXCEPT ON)
+    message(STATUS "Detected support for conditional noexcept")
+endif()
+
+if(cxx_constexpr IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+    set(RING_BUFFER_CONSTEXPR ON)
+    message(STATUS "Detected support for constexpr")
+endif()
+
+try_compile(constexpr-destructors-compile ${CMAKE_BINARY_DIR}/detect ${CMAKE_SOURCE_DIR}/detect/constexpr_destructors.cpp
+    CXX_STANDARD ${CMAKE_CXX_STANDARD}
+    CXX_STANDARD_REQUIRED ${CMAKE_CXX_STANDARD_REQUIRED}
+    CXX_EXTENSIONS ${CMAKE_CXX_EXTENSIONS}
+)
+if(constexpr-destructors-compile)
+    set(RING_BUFFER_CONSTEXPR_DESTRUCTORS ON)
+    message(STATUS "Detected support for constexpr destructors")
+endif()