(There doesn't seem to be a component for the applications in the tools repository).
The version of ddmangle included with dmd needs rebuilding (on at least OS X, possibly other platforms). The version included with dmd 2.057 gives the following:
$ echo "_D6object8__assertFiZv" | ddmangle
_D6object8__assertFiZv
However getting the source from github and compiling it gives:
$ echo "_D6object8__assertFiZv" | ./ddmangle
void object.__assert(int)
As expected. This was fixed in July of last year - https://github.com/D-Programming-Language/tools/commit/8de843daf8b4d856989f54f3af969a6efd3a19b7#ddemangle.d
It's still beyond me why a clean package isn't built for each release from git, rather than using a dirty directory which causes old things to creep in time after time.