Comment out building libunwind

This failed building for me, so skip it for now.

Dockerfile

@@ -144,8 +144,8 @@ RUN cd libunwind && mkdir build && cd build && \
         -DLIBUNWIND_ENABLE_SHARED=OFF \
         ..
 
-RUN cd libunwind/build && make -j4 
-RUN cd libunwind/build && make install
+#RUN cd libunwind/build && make -j4
+#RUN cd libunwind/build && make install
 
 RUN cd libcxx && mkdir build && cd build && \
     CXXFLAGS="-nodefaultlibs -D_GNU_SOURCE -D_LIBCPP_HAS_NO_CONSTEXPR" \