populate_sdk_ext.bbclass: avoid populating tools twice

populate_sdk_ext.bbclass: avoid populating tools twice

When running `bitbake -c populate_sdk_ext ...` for an image
recipe inheriting populate_sdk_qt5, `nativesdk-qemu-helper` is
deployed via `nativesdk-packagegroup-sdk-host`, which already
contains some of the tools (by name: "oe-find-native-sysroot
runqemu*").

To avoid error like:
    Configuring nativesdk-packagegroup-qt5-toolchain-host.

    NOTE: Running intercept scripts:
    NOTE: > Executing update_gio_module_cache-nativesdk intercept ...
    NOTE: + [ True = False ]
    + qemu-x86_64 -r 3.2.0 -E LD_LIBRARY_PATH=/home/sno/gpw-community-bsp/mops-yocto-platform/tmp/work/fischer-poky-linux/updatable-app-image/1.0-r0/sdk-ext/image/opt/mops/2.5+snapshot/sysroots/x86_64-pokysdk-linux/usr/lib:/home/sno/gpw-community-bsp/mops-yocto-platform/tmp/work/fischer-poky-linux/updatable-app-image/1.0-r0/sdk-ext/image/opt/mops/2.5+snapshot/sysroots/x86_64-pokysdk-linux/lib -L /home/sno/gpw-community-bsp/mops-yocto-platform/tmp/work/fischer-poky-linux/updatable-app-image/1.0-r0/sdk-ext/image /home/sno/gpw-community-bsp/mops-yocto-platform/tmp/work/fischer-poky-linux/updatable-app-image/1.0-r0/sdk-ext/image/opt/mops/2.5+snapshot/sysroots/x86_64-pokysdk-linux/usr/libexec/nativesdk-gio-querymodules /home/sno/gpw-community-bsp/mops-yocto-platform/tmp/work/fischer-poky-linux/updatable-app-image/1.0-r0/sdk-ext/image/opt/mops/2.5+snapshot/sysroots/x86_64-pokysdk-linux/usr/lib/gio/modules/

    NOTE: Executing copy_buildsystem ...
    DEBUG: Executing python function copy_buildsystem
    NOTE: Generating sstate task list...
    NOTE: Generating sstate-cache...
    NOTE: Generating sstate-cache...
    DEBUG: Python function copy_buildsystem finished
    NOTE: Executing install_tools ...
    DEBUG: Executing shell function install_tools
    Traceback (most recent call last):
      File "/home/sno/gpw-community-bsp/sources/poky/scripts/lnr", line 21, in <module>
	os.symlink(target, linkname)
    FileExistsError: [Errno 17] File exists: '../../../../layers/poky/scripts/oe-find-native-sysroot' -> '/home/sno/gpw-community-bsp/mops-yocto-platform/tmp/work/fischer-poky-linux/updatable-app-image/1.0-r0/sdk-ext/image//opt/mops/2.5+snapshot/sysroots/x86_64-pokysdk-linux/usr/bin/oe-find-native-sysroot'
    WARNING: exit code 1 from a shell command.
    DEBUG: Python function do_populate_sdk_ext finished

only add those tools unpackaged to the deployment which are
still missing.

Signed-off-by: Jens Rehsack <sno@netbsd.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>