build-libcxx: Explicitly enable LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS

This used to be the default before, but has changed in the
latest master version of libcxx.

Previously, both libcxx and libcxxabi enabled it by default, but
we used to explicitly disable it on the libcxxabi side (and rely
on the default for libcxx). Instead explicitly set the intended
configuration state for both parts.

build-libcxx.sh

@@ -202,6 +202,7 @@ build_all() {
             -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=OFF \
             -DLIBCXX_ENABLE_FILESYSTEM=OFF \
             -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=TRUE \
+            -DLIBCXX_ENABLE_NEW_DELETE_DEFINITIONS=ON \
             -DLIBCXX_CXX_ABI=libcxxabi \
             -DLIBCXX_CXX_ABI_INCLUDE_PATHS=../../libcxxabi/include \
             -DLIBCXX_CXX_ABI_LIBRARY_PATH=../../libcxxabi/build-$arch-$type/lib \