Log Message:
x11/gtkada: Build with USE_LANGUAGES+= ada

1) Remove lang/gnat-aux dependency
2) USE_LANGUAGES+= ada (invokes lang/gcc-aux dependency)
3) USE_TOOLS+= pkg-config (remove hardcoded PATH)
4) Restore use of pkgsrc wrappers
5) Fix bad paths of bin/gate (discovered by updated PKG_DEVELOPER=yes)
6) Use @pkgdir for required empty directory instead of .IGNOREME
7) Add -lgnat for shared libraries, required in this build configuration