include/dmlc/omp.h:13:9: warning: Warning: OpenMP is not available, project will be compiled into single-thread code. Use
OpenMP-enabled compiler to get benefit of multi-threading. [-W#pragma-messages]

pragma message("Warning: OpenMP is not available, " \

...

NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [bin/im2rec] Error 1