title: The C++ compiler does not support C++11 (e.g. std::unique_ptr). building OpenWRT
body: <p>I am using instructions <a href="https://openwrt.org/docs/guide-user/additional-software/beginners-build-guide#compiling_openwrt" rel="noreferrer">here</a> and <a href="https://openwrt.org/docs/guide-developer/quickstart-build-images" rel="noreferrer">here</a> to build OpenWRT in ubuntu but am getting:</p>
  
  <pre><code>make[4]: Entering directory '~/openwrt/build_dir/host/cmake-3.11.1/Bootstrap.cmk'
  make[4]: 'cmake' is up to date.
  make[4]: Leaving directory '~/openwrt/build_dir/host/cmake-3.11.1/Bootstrap.cmk'
  loading initial cache file ~/openwrt/build_dir/host/cmake-3.11.1/Bootstrap.cmk/InitialCacheFlags.cmake
  CMake Error at CMakeLists.txt:92 (message):
    The C++ compiler does not support C++11 (e.g.  std::unique_ptr).
  
  
  -- Configuring incomplete, errors occurred!
  </code></pre>
  
  <p>There was a solution to a similar problem <a href="https://stackoverflow.com/questions/10851247/how-to-activate-c-11-in-cmake">here</a>, however it is not clear to me which CMakeLists.txt file is the 'root' in my case. Not seeing much on the OpenWRT forums (or search engines in general) about this fail.</p>
  
  <p>The impression I get is that the CMake installation is downloaded by the OpenWRT builder itself, as I do not have CMake installed and installing cmake resolved nothing.</p>
  
  <p>Tried checking out latest OpenWRT v18.06.2. When that failed to build I deleted the cloned directory and tried v18.06.0-rc2. There was no improvement.</p>
  
  <p>Also tried </p>
  
  <blockquote>
    <p>export CMAKE_CXX_STANDARD=11</p>
  </blockquote>
  
  <p>before running 'make'
  ... it did not resolve the issue.</p>
  
  <p>The state of my g++ install:</p>
  
  <pre><code>$ g++ -v
  Using built-in specs.
  COLLECT_GCC=g++
  COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
  OFFLOAD_TARGET_NAMES=nvptx-none
  OFFLOAD_TARGET_DEFAULT=1
  Target: x86_64-linux-gnu
  Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-27ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
  Thread model: posix
  gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
  </code></pre>
  
  <p>Well, that's 5 hours I'm out of ideas. Could this be a misconfiguration or a bug on the dev end?</p>
  
  <p>If a misconfiguration, what could be set up wrong?</p>