libevent2: Don't expose debug global data as extern(C)
libevent2: Don't expose debug global data as extern(C)

There is no reason for them to be extern(C).
However, they can be easily corrupted / misinterpreted as
their name would be quite trivial in the resulting binary.

Related to rejectedsoftware/vibe.d#1475

chalucha/vibe.d,etcimon/vibe.d,Geod24/vibe.d,rejectedsoftware/vibe.d,DBankov/vibe.d,etcimon/vibe.d,gedaiu/vibe.d,AndreyMZ/vibe.d