(see https://github.com/grocsvs/idba#comments explaining why this fork is necessary)
To build:
./build.sh
./configure
make
then copy the binary idba_ud into your $PATH.
Please note that if you are compiling on macOS, you will need to use an OpenMP-compatible compiler (as of this writing, the Apple-provided clang compiler does not support OpenMP). See http://stackoverflow.com/questions/29057437/compile-openmp-programs-with-gcc-compiler-on-os-x-yosemite