Example build failure is missing `VCMI_LIB_NAMESPACE_BEGIN` declaration:
[ 0%] Building CXX object lib/CMakeFiles/vcmi.dir/spells/ObstacleCasterProxy.cpp.o
In file included from lib/spells/ProxyCaster.h:13,
from lib/spells/ObstacleCasterProxy.h:11,
from lib/spells/ObstacleCasterProxy.cpp:11:
lib/../include/vcmi/spells/Caster.h:13:1: error: 'VCMI_LIB_NAMESPACE_BEGIN' does not name a type
13 | VCMI_LIB_NAMESPACE_BEGIN
| ^~~~~~~~~~~~~~~~~~~~~~~~