clang: error: linker command failed with exit code 1

[DMGoldstein]

At what appears to be almost the end of the installation process, I get the following error:

[100%] Linking CXX executable ../biphy
Undefined symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [../biphy] Error 1
make[1]: *** [CMakeFiles/biphy.dir/all] Error 2
make: *** [all] Error 2

I've searched around for a solution, but so far have not been able to figure out how to get around this.