CMake: add mechanism to deprecate code

cmake/mainSetup.cmake

@@ -5,6 +5,14 @@ include(GNUInstallDirs)
 include(CheckFunctionExists)
 include(GenerateExportHeader)
 include(CMakeDependentOption)
+include(WriteCompilerDetectionHeader)
+
+write_compiler_detection_header(
+    FILE exiv2lib_compiler_detection.h
+    PREFIX EXIV2
+    COMPILERS GNU Clang AppleClang MSVC
+    FEATURES cxx_attribute_deprecated
+)
 
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)