toolchain: Correct test for external tools symlink creation

When the external tools chain is installed in a path that match one of
the first case test, all symlink are created to the external
wrapper. The proposed solution is to test only the base name not the
full path.

Signed-off-by: Stany MARCEL <stanypub@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>