You seem to have exactly the same problem as the one described in this bug report (right down to the same toolbar icons being missing):
https://github.com/vim/vim/issues/567
This was apparently fixed in 7.4.1138, but -current has 7.4.1530. The patch introduced by the 1138 commit is still in -current's vim-gvim source tarball too... What happens if you run "gvim -N -u NONE -U NONE", per the original bug report?