The file "src/aiori-NCMPI.c" uses numTasksWorld as the process which is declared in "src/ior.h". In "src/mdtest.c", NCMPI backend will be called if IOR configured with ncmpi enabled but numTasksWorld was not defined in "src/mdtest.c". So it will cause a compiler error like below:
mdtest-aiori-NCMPI.o: In function `NCMPI_Xfer':
/home/parallels/Documents/ior/src/aiori-NCMPI.c:272: undefined reference to `numTasksWorld'