A BuildMode indicates the sort of object we are building:

"exe": build a main package and everything it imports into an executable.
"c-shared": build a main package, plus all packages that it imports, into a
  single C shared library. The only callable symbols will be those functions
  marked as exported.
"shared": combine all packages passed on the command line, and their
  dependencies, into a single shared library that will be used when
  building with the -linkshared option.

BuildMode is referenced in 1 repository