The second is the SWIG program, which is a general tool for
interfacing between languages. For information on SWIG see
http://swig.org/. When running go build, any file with a .swig
extension will be passed to SWIG. Any file with a .swigcxx extension
will be passed to SWIG with the -c++ option.

When either cgo or SWIG is used, go build will pass any .c, .m, .s, .S
or .sx files to the C compiler, and any .cc, .cpp, .cxx files to the C++

	case ".h", ".hh", ".hpp", ".hxx":
		return &p.HFiles
	case ".f", ".F", ".for", ".f90":
		return &p.FFiles
	case ".s", ".S", ".sx":
		return &p.SFiles
	case ".swig":
		return &p.SwigFiles
	case ".swigcxx":
		return &p.SwigCXXFiles
	case ".syso":
		return &p.SysoFiles
	}
	return nil
}

var errNoModules = errors.New("not using modules")

func findImportComment(data []byte) (s string, line int) {

        FFiles            []string   // .f, .F, .for and .f90 Fortran source files
        SFiles            []string   // .s source files
        SwigFiles         []string   // .swig files
        SwigCXXFiles      []string   // .swigcxx files
        SysoFiles         []string   // .syso object files to add to archive
        TestGoFiles       []string   // _test.go files in package
        XTestGoFiles      []string   // _test.go files outside package