/usr/include/mongo/platform/ is in libmongoclient-dev 1.1.2-6ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/mongo/platform/atomic_intrinsics.h
/usr/include/mongo/platform/atomic_intrinsics_gcc_atomic.h
/usr/include/mongo/platform/atomic_intrinsics_gcc_intel.h
/usr/include/mongo/platform/atomic_intrinsics_gcc_sync.h
/usr/include/mongo/platform/atomic_intrinsics_win32.h
/usr/include/mongo/platform/atomic_word.h
/usr/include/mongo/platform/atomic_word_cxx11.h
/usr/include/mongo/platform/atomic_word_intrinsics.h
/usr/include/mongo/platform/compiler.h
/usr/include/mongo/platform/compiler_gcc.h
/usr/include/mongo/platform/compiler_msvc.h
/usr/include/mongo/platform/cstdint.h
/usr/include/mongo/platform/endian.h
/usr/include/mongo/platform/float_utils.h
/usr/include/mongo/platform/hash_namespace.h
/usr/include/mongo/platform/strnlen.h
/usr/include/mongo/platform/unordered_map.h
/usr/include/mongo/platform/windows_basic.h