"buildheader/db.h:326:1: warning: empty struct has size 0 in C, size 1 in C++ [-Wextern-c-compat]"

```
cmake -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTING=OFF -DUSE_VALGRIND=OFF
...
make
...
[ 24%] Building CXX object util/CMakeFiles/util.dir/context.cc.o
In file included from /Users/laurynas/percona/ft-index/util/context.cc:41:
In file included from /Users/laurynas/percona/ft-index/util/context.h:43:
/Users/laurynas/percona/ft-index/obj-debug/buildheader/db.h:326:1: warning: empty struct has size 0 in C, size 1 in C++ [-Wextern-c-compat]
struct __toku_db_lsn {
^
1 warning generated.
```
repeated dozens of times