GO_EXTLINK_ENABLED
		Whether the linker should use external linking mode
		when using -linkmode=auto with code that uses cgo.
		Set to 0 to disable external linking mode, 1 to enable it.

		// The environment variable GO_EXTLINK_ENABLED controls the
		// default value of -linkmode. If it is not set when the
		// linker is called we take the value it was set to when
		// cmd/link was compiled. (See make.bash.)

	iscgo = ctxt.LibraryByPkg["runtime/cgo"] != nil

	if ctxt.LinkMode == LinkExternal && !iscgo && !(buildcfg.GOOS == "darwin" && ctxt.BuildMode != BuildModePlugin && ctxt.Arch.Family == sys.AMD64) {
		// This indicates a user requested -linkmode=external.
		// The startup code uses an import of runtime/cgo to decide
		// whether to initialize the TLS.  So give it one. This could
		// be handled differently but it's an unusual case.
		if lib := loadinternal(ctxt, "runtime/cgo"); lib != nil && lib.Shlib == "" {
			if ctxt.BuildMode == BuildModeShared || ctxt.linkShared {
				Exitf("cannot implicitly include runtime/cgo in a shared library")
			}
			for ; i < len(ctxt.Library); i++ {
				lib := ctxt.Library[i]
				if lib.Shlib == "" {
					loadobjfile(ctxt, lib)
				}
			}
		}
	}