/usr/lib/x86_64-linux-gnu/ is in libbullet-dev 2.87+dfsg-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/x86_64-linux-gnu/libBullet3Dynamics.so
/usr/lib/x86_64-linux-gnu/libBullet3Geometry.so
/usr/lib/x86_64-linux-gnu/libLinearMath.so
/usr/lib/x86_64-linux-gnu/cmake/
/usr/lib/x86_64-linux-gnu/cmake/bullet/
/usr/lib/x86_64-linux-gnu/cmake/bullet/BulletConfig.cmake
/usr/lib/x86_64-linux-gnu/cmake/bullet/UseBullet.cmake
/usr/lib/x86_64-linux-gnu/pkgconfig/
/usr/lib/x86_64-linux-gnu/pkgconfig/bullet.pc
/usr/lib/x86_64-linux-gnu/libBullet3Collision.so
/usr/lib/x86_64-linux-gnu/libBullet3Common.so
/usr/lib/x86_64-linux-gnu/libBullet3OpenCL_clew.so
/usr/lib/x86_64-linux-gnu/libBulletCollision.so
/usr/lib/x86_64-linux-gnu/libBulletDynamics.so
/usr/lib/x86_64-linux-gnu/libBulletSoftBody.so