devel/freebsd-sysroot: Unbreak build as root

> Extracting for amd64-freebsd-sysroot-a2021.09.12

> SHA256 Checksum OK for rust/bootstrap/amd64/12.2-RELEASE/base.txz.

chmod: /wrkdirs/usr/ports/devel/freebsd-sysroot/work-amd64/stage/usr/local/freebsd-sysroot/amd64/lib/libthr.so.3: Operation not permitted
chmod: /wrkdirs/usr/ports/devel/freebsd-sysroot/work-amd64/stage/usr/local/freebsd-sysroot/amd64/lib/libc.so.7: Operation not permitted
chmod: /wrkdirs/usr/ports/devel/freebsd-sysroot/work-amd64/stage/usr/local/freebsd-sysroot/amd64/lib/libcrypt.so.5: Operation not permitted
chmod: /wrkdirs/usr/ports/devel/freebsd-sysroot/work-amd64/stage/usr/local/freebsd-sysroot/amd64/usr/lib/librt.so.1: Operation not permitted