Silence some libcxx versions' warnings about std::experimental deprecation

We do our own availability detection in CMake, so we don't care about the deprecation.

src/core/Any.h

@@ -25,6 +25,7 @@
 #if defined(WALBERLA_USE_STD_ANY)
 #include <any>
 #elif defined(WALBERLA_USE_STD_EXPERIMENTAL_ANY)
+#undef _LIBCPP_WARN_ON_DEPRECATED_EXPERIMENTAL_HEADER
 #include <experimental/any>
 #else
 #include <boost/any.hpp>

src/core/Filesystem.h

@@ -25,6 +25,7 @@
 #if defined(WALBERLA_USE_STD_FILESYSTEM)
 #include <filesystem>
 #elif defined(WALBERLA_USE_STD_EXPERIMENTAL_FILESYSTEM)
+#define _LIBCPP_NO_EXPERIMENTAL_DEPRECATION_WARNING_FILESYSTEM
 #include <experimental/filesystem>
 #else
 #include <boost/filesystem.hpp>

src/core/Optional.h

@@ -25,6 +25,7 @@
 #if defined(WALBERLA_USE_STD_OPTIONAL)
 #include <optional>
 #elif defined(WALBERLA_USE_STD_EXPERIMENTAL_OPTIONAL)
+#undef _LIBCPP_WARN_ON_DEPRECATED_EXPERIMENTAL_HEADER
 #include <experimental/optional>
 #else
 #include <boost/optional.hpp>