tools: libtool: do not symlink files in bootstrap

tools: libtool: do not symlink files in bootstrap

Another instance of files in build_dir symlinking to staging_dir. While
the symlinks do not currently cause any bugs in the libtool package,
such symlinks were found to make the build more fragile, as writing to
the symlink may accidentally modify the shared file in staging_dir. Pass
--copy to bootstrap to disable the symlinking.

Link: https://github.com/openwrt/openwrt/pull/15825
Signed-off-by: Matthias Schiffer <[email protected]>