synch: add an internal lock & helper macros to protect the dependency graph
synch: add an internal lock & helper macros to protect the dependency graph

The dependency graph will require a lock to avoid concurrent modifications
by different threads.

Currently unused.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc