I am trying to build the mongo-tools 4.2.1 version source. Getting below error while compiling:

I cloned the mongo-tools from https://github.com/mongodb/mongo-tools/tree/r4.2.1 to the go directory under src/github.com/mongodb.

after setting the goroot , executing ./build.sh

Note: Using cygwin to compile.
 
{{Building bsondump...bsondump\bsondump.go:21:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\db
bsondump\bsondump.go:22:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\failpoint
bsondump\bsondump.go:23:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\json
bsondump\main\bsondump.go:13:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\log
bsondump\bsondump.go:25:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\options
bsondump\main\bsondump.go:14:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\signals
bsondump\main\bsondump.go:15:2: cannot find package "." in: C:\golang\go1.12\src\github.com\mongodb\mongo-tools-common\util
bsondump\bsondump.go:18:2: cannot find package "." in: C:\golang\go1.12\src\go.mongodb.org\mongo-driver\bson
bsondump\bsondump.go:19:2: cannot find package "." in: C:\golang\go1.12\src\go.mongodb.org\mongo-driver\bson\bsontypeError building bsondump}}

{{}}

Please let me know why this error is.