Recent setup for 7.6 does not support
  bfd_target_elf_flavour
instead only supports
  bfd_target_aout_flavour
  bfd_target_coff_flavour
  bfd_target_ecoff_flavour.
To fix this, we need
+CONFIGURE_ENV+=                gdb_cv_var_elf=yes
as found in native gdb setup (pkgsrc Makefile).