The C++11 standard appears to break backwards compatibility with previous standards, by declaring the bool conversion operator for streams as explicit.
This breaks the HiScore1 code in 0.6.4 for GNU GCC versions 5 and above, as exemplified abstractly here.
Attached to this post is a patch for src/include/hiscore1.h that should fix the problem.
$ basename `pwd`
trigger-rally-0.6.4
$ ls
bin data doc hiscore1.h.patch src
$ patch -p 0 -i hiscore1.h.patch
$ cd src
$ make
EDIT: fixed the patch, added usage information.
Should be fixed in 0.6.5 with this commit:
https://sourceforge.net/p/trigger-rally/code/798/tree//src/include/hiscore1.h?diff=5076ed3b71b75b610140215e:797
@Ferdinand: indeed this problem was fixed in version 0.6.5, however this ticket is to be kept open for legacy users of 0.6.4 who may need the patch.