package/llvm: add dependency on shared libraries

llvm generates libLLVM.so, so it won't work if BR2_STATIC_LIBS is set

Also propagate llvm dependency to mesa3d.

Link to report from autobuilders:
http://lists.busybox.net/pipermail/buildroot/2018-April/218296.html



Signed-off-by: Valentin Korenblit <valentin.korenblit@smile.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>