Use buildroot host gdb, consider QEMU and target GDB but give up for now

run

@@ -2,6 +2,8 @@
 set -e
 cd buildroot
 make BR2_EXTERNAL="$(pwd)/../kernel_module" qemu_x86_64_defconfig
+# Can't get rid of this for now.
+# http://stackoverflow.com/questions/44078245/is-it-possible-to-use-config-fragments-with-buildroots-config
 cat ../buildroot_config_fragment >> .config
 env -u LD_LIBRARY_PATH make BR2_JLEVEL="$(($(nproc) - 2))" kernel_module-rebuild all
 cd ..