$ (cd build && LANG=C CXX=g++ CXX_FLAGS='-O1' make -j12)
[  0%] mo update
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$HOME/share/src/games/minetest/src/unittest/test_servermodmanager.cpp: In member function 'virtual void TestServerModManager::runTests(IGameDef*)':
$HOME/share/src/games/minetest/src/unittest/test_servermodmanager.cpp:64:30: error: 'TEST_MOD_PATH' was not declared in this scope
   64 |  setenv("MINETEST_MOD_PATH", TEST_MOD_PATH, 1);
      |                              ^~~~~~~~~~~~~
[ 47%] Building CXX object src/CMakeFiles/minetest.dir/util/metricsbackend.cpp.o
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make[2]: *** [src/CMakeFiles/minetest.dir/build.make:2760: src/CMakeFiles/minetest.dir/unittest/test_servermodmanager.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:863: src/CMakeFiles/minetest.dir/all] Error 2
make: *** [Makefile:171: all] Error 2