Pass the CC variable to the example Makefiles

Pass the CC variable to the example Makefiles

Cross-compilation fails when using the --host configure option
since the cross-compiler is not invoked by the hand-made Makefiles
in doc/examples.

The CC variable must be passed explicitly to ensure the host's
default compiler is not invoked.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>