MFC	r263973;

ddb: Minor style cleanups.

#define should be followed by tab.
MFC	r264121;
gcc: define __block when block support is enabled

This mimics the behaviour in clang and lets us build cleanly
the libdispatch port on platforms where the base gcc is still
the default compiler.

Bump __FreeBSD_version for ports.

Tested by:	theraven