Code review comment for lp:~nick-dedekind/qtmir/miral-DisplayConfigurationStorage

I get this error when using Ninja, can you have a look:

FAILED: src/platforms/mirserver/miral/CMakeFiles/miral-prototypes.dir
/usr/lib/ccache/c++ -DQT_NO_DEBUG -DQT_NO_KEYWORDS -DQT_USE_QSTRINGBUILDER -DQT_USING_GL -Isrc/platforms/mirserver/miral -I../src/platforms/mirserver/miral -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/mirserver -isystem /usr/include/mirclient -isystem /usr/include/mircookie -isystem /usr/include/mirplatform -isystem /usr/include/mircommon -isystem /usr/include/uuid -isystem /usr/include/mircore -fPIC -Wall -fno-strict-aliasing -Werror -Wextra -O2 -g -DNDEBUG -std=gnu++14 -MD -MT src/platforms/mirserver/miral/CMakeFiles/miral-prototypes.dir -MF src/platforms/mirserver/miral/CMakeFiles/miral-prototypes.dir/.d -o src/platforms/mirserver/miral/CMakeFiles/miral-prototypes.dir -c /home/gerry/dev/projects/qtmir/miral-DisplayConfigurationStorage/BUILD/src/platforms/mirserver/miral/miral-prototypes_automoc.cpp
Assembler messages:
Fatal error: can't create src/platforms/mirserver/miral/CMakeFiles/miral-prototypes.dir: Is a directory