HFS+ on MacOS X is not a case sensitive filesystem... but it is case-preserving. When building imfeat on MacOS X, a linker error is generated because autocorrelogram.c and Autocorrelogram.cpp both build to autocorrelogram.o/Autocorrelogram.o.
Renaming Autocorrelogram.cpp to "Auto_correlogram.cpp" as a quick fix resolved the problem.