Most variables used in the sound engine were static globals, as they are used in the static sound mixing function. The global variables are replaced by member variables, by passing the sound interface as user-data for the SDL mixing callback. The `Mix` function is made a public member function of `ISound` instead of being exposed using `ISoundMixFunc GetSoundMixFunc()`.
This allows to remove the direct dependency of the engine sound on the engine video, by instead passing the sound mixing function as a lambda to the engine video in the engine client.
The old WavPack reader function interface does support passing a user-data pointer to the callback function, so global variables are still used here.
Not planning to do this automatically, but at least cleaning it up once
provides some benefit. Every header should include what it uses.
$ for i in src/**/*.h; do j=${i#"src/"}; echo $j; echo "#include <$j>\nint main() { return 0; }" | /usr/bin/c++ -DCONF_OPENSSL -DCONF_SQL -DCONF_VIDEORECORDER -DCONF_WAVPACK_CLOSE_FILE -DCONF_WAVPACK_OPEN_FILE_INPUT_EX -DGAME_RELEASE_VERSION=\"15.0.5\" -DGLEW_STATIC -D_FORTIFY_SOURCE=2 -I/usr/include/freetype2 -I/usr/include/opus -I/usr/include/SDL2 -I/usr/include/wavpack -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libmount -I/usr/include/blkid -Isrc -I/usr/include/mysql -I/home/deen/sys/include/ -O2 -g -DNDEBUG -fdiagnostics-color=always -fstack-protector-all -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wformat=2 -Wno-nullability-completeness -Wduplicated-cond -Wduplicated-branches -Wlogical-op -Wrestrict -std=gnu++11 -o /dev/null -x c++ -; done
Ignored: tuning.h, variables.h, config_common.h, mapitems_ex_types.h, mapbugs_list.h, protocol7.h, teehistorian_ex_chunks.h, protocol_ex_msgs.h, config.h, config_variables.h, external, keynames.h
