include: autotools: do not symlink files in autoreconf

include: autotools: do not symlink files in autoreconf

In Gluon's Github Actions CI, we were occasionally seeing bizarre build
errors that looked like a config.sub file had been corrupted, or changed
while it was being executed.

The cause turned out to be an interaction of the symlinks created by
autoreconf (pointing from individual tools' build dirs into
`staging_dir/host/share/automake-1.16`) and OpenWrt's host-build.mk,
which replaced config.guess and config.sub *after* autoreconf. The
result was that the replacement of these files ended up following the
symlinks and writing the files in `staging_dir/host/share/automake-1.16`
instead of a package's build dir. This could cause other packages' builds
to fail if they were currently executing the scripts while they were
being written.

To fix this, disable autoreconf's symlinking feature, so that modifying
these files in a package's build directory can't accidentally affect the
staged versions.

Link: https://github.com/openwrt/openwrt/pull/15825
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>