Note: after this, the header guards will be like "SRC_ENGINE_FOO_H" in accordance with Google C++ style. We understand that in the macOS version, the source is located in Source/. However the source in fcitx5-mcbopomofo is in src/. Since we do most of the linting and tidying there, we think it makes sense to use the header guards this way.
This carries over several fixes there.
Note: after this, the header guards will be like "SRC_ENGINE_FOO_H" in accordance with Google C++ style. We understand that in the macOS version, the source is located in Source/. However the source in fcitx5-mcbopomofo is in src/. Since we do most of the linting and tidying there, we think it makes sense to use the header guards this way.