are not subject to the security limitations described above.

All the cgo CPPFLAGS and CFLAGS directives in a package are concatenated and
used to compile C files in that package. All the CPPFLAGS and CXXFLAGS
directives in a package are concatenated and used to compile C++ files in that
package. All the CPPFLAGS and FFLAGS directives in a package are concatenated

// but are costly to evaluate.
func ExtraEnvVarsCostly() []cfg.EnvVar {
	b := work.NewBuilder("")
	defer func() {
		if err := b.Close(); err != nil {
			base.Fatal(err)
		}
	}()

	cppflags, cflags, cxxflags, fflags, ldflags, err := b.CFlags(&load.Package{})
	if err != nil {
		// Should not happen - b.CFlags was given an empty package.
		fmt.Fprintf(os.Stderr, "go: invalid cflags: %v\n", err)
		return nil

			}
			args[i] = arg
		}

		switch verb {
		case "CFLAGS", "CPPFLAGS", "CXXFLAGS", "FFLAGS", "LDFLAGS":
			// Change relative paths to absolute.
			ctxt.makePathsAbsolute(args, di.Dir)
		}

		switch verb {
		case "CFLAGS":
			di.CgoCFLAGS = append(di.CgoCFLAGS, args...)
		case "CPPFLAGS":
			di.CgoCPPFLAGS = append(di.CgoCPPFLAGS, args...)
		case "CXXFLAGS":

	}
	return args
}

// CFlags returns the flags to use when invoking the C, C++ or Fortran compilers, or cgo.
func (b *Builder) CFlags(p *load.Package) (cppflags, cflags, cxxflags, fflags, ldflags []string, err error) {
	if cppflags, err = buildFlags("CPPFLAGS", "", p.CgoCPPFLAGS, checkCompilerFlags); err != nil {
		return
	}
	if cflags, err = buildFlags("CFLAGS", DefaultCFlags, p.CgoCFLAGS, checkCompilerFlags); err != nil {