Can't build, seems dependencies problem

```
# github.com/fogleman/triangle
/tmp/go-build161286829/b064/_x003.o: In function `parsecommandline':
../../../../pkg/mod/github.com/fogleman/triangle@v0.0.0-20170810015530-d3acf44b0c9b/triangle.c:3327: undefined reference to `cos'
../../../../pkg/mod/github.com/fogleman/triangle@v0.0.0-20170810015530-d3acf44b0c9b/triangle.c:3528: undefined reference to `sqrt'
etc ...
```