buildroot

pkg-cmake: enable toolchain install staging phase

Really fix commit 6729050f3a49dba42d2d881d31dbefd6b82b8dad

That commit added a script to "toolchain" post install staging hooks.
This will only be executed if TOOLCHAIN_INSTALL_STAGING is set to YES.

Signed-off-by: Stefan Becker <chemobejk@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>