For what it's worth, I've also just seen a test failure in tests/upmendex on i386, during a test rebuild of all packages using gcc-defaults and glibc from experimental:
FAIL: tests/upmendex ==================== This is upmendex version 0.50 (TeX Live 2016). Scanning input file ../../../texk/upmendex/tests/foo.idx....done (3 entries accepted, 0 rejected). 3 entries accepted, 0 rejected. Sorting index....done(0 comparisons). Sorting pages....done(4 comparisons). Making index file....done. 0 warnings, written in foo.ilg1. Output written in foo.ind1. This is upmendex version 0.50 (TeX Live 2016). Scanning dictionary file ../../../texk/upmendex/tests/uni.dict....done. Scanning input file ../../../texk/upmendex/tests/uni.idx....done (8 entries accepted, 0 rejected). 8 entries accepted, 0 rejected. Sorting index....done(24 comparisons). Sorting pages....done(0 comparisons). Making index file.Segmentation fault FAIL tests/upmendex.test (exit status: 1) -- Daniel Schepler