CMake/macOS: Restore TIFF's optional status.

{rB1f6b7387ad01}

build_files/cmake/platform/platform_apple.cmake

@@ -235,8 +235,14 @@ find_package(PNG REQUIRED)
 set(JPEG_ROOT ${LIBDIR}/jpeg)
 find_package(JPEG REQUIRED)
 
-set(TIFF_ROOT ${LIBDIR}/tiff)
-find_package(TIFF REQUIRED)
+if(WITH_IMAGE_TIFF)
+  set(TIFF_ROOT ${LIBDIR}/tiff)
+  find_package(TIFF)
+  if(NOT TIFF_FOUND)
+    message(WARNING "TIFF not found, disabling WITH_IMAGE_TIFF")
+    set(WITH_IMAGE_TIFF OFF)
+  endif()
+endif()
 
 if(WITH_BOOST)
   set(Boost_NO_BOOST_CMAKE ON)