--std=c++11 fails on master

[Pavel Sanda]

On Sun, Oct 25, 2020 at 12:48:14PM -0400, Scott Kostyshak wrote:
> On Sun, Oct 25, 2020 at 08:49:05AM +0100, Jean-Marc Lasgouttes wrote:
> > Le 25 octobre 2020 07:15:17 GMT+01:00, Scott Kostyshak <skostysh at lyx.org> a écrit :
> > >Do we require c++14 now? If I force --std=c++11 I get errors.
> > 
> > 
> > It is supposed to work with c++11. What are the errors?
> 
> [ 25%] Building CXX object src/support/CMakeFiles/support.dir/FileMonitor.cpp.o
> cd /home/scott/lyxbuilds/temp/CMakeBuild/src/support && /usr/bin/c++  -DBOOST_USER_CONFIG="<config.h>" -DHUNSPELL_STATIC -DQT_CORE_LIB -DQT_GUI_LIB -I/home/scott/lyxbuilds/temp/CMakeBuild -I/home/scott/lyxbuilds/temp/repo/src -I/usr/include/enchant -I/home/scott/lyxbuilds/temp/repo/3rdparty/hunspell/1.7.0/src/hunspell -I/home/scott/lyxbuilds/temp/repo/3rdparty/hunspell/1.7.0/src -I/home/scott/lyxbuilds/temp/repo/3rdparty/boost -I/home/scott/lyxbuilds/temp/repo/src/support -I/home/scott/lyxbuilds/temp/CMakeBuild/src/support -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++ -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui  -Wall -Wunused-parameter  -DENABLE_ASSERTIONS=1 -D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC -fno-strict-aliasing  -O0 -g3 -D_DEBUG   -fPIC -std=c++11 -o CMakeFiles/support.dir/FileMonitor.cpp.o -c /home/scott/lyxbuilds/temp/repo/src/support/FileMonitor.cpp
> In file included from /home/scott/lyxbuilds/temp/repo/src/support/FileMonitor.cpp:19:
> /home/scott/lyxbuilds/temp/repo/src/support/unique_ptr.h:24:28: error: ???std::make_unique??? has not been declared
>    24 | namespace lyx { using std::make_unique; }

Sounds like missing include due to the recent headers cleanup.. P