Yes, it's not an infinite loop; it just takes an inordinate amount of time.
The code that triggers this seems to be a long sequence of assignments initialising elements of a multi-dimensional array. There are some big variations in the build times on some other architectures, too. For example on powerpc, "praetorius" built rnahybrid 2.1-2 in 3m, and 2.1.2-1 in 46m, the former with GCC 4.3, the latter with GCC 5.3, though obviously there are other differences in that comparison. Also the differences in build times between architectures look suspicious when compared with the differences in building other packages.