Fix flags for default BSD tar

[fivitti]

Hi!

I work on FreeBSD 13.1 and use FPM to prepare a package for this system.
After running FPM, I get the above error:

pid 1174 exit 1
{:timestamp=>"2022-08-17T16:19:18.544663+0000", :message=>"Process failed: tar failed (exit code 1). Full command was:[\"tar\", \"-Jcf\", \"agent-1.5.0.220817161918.txz\", \"-C\", \"/tmp/package-dir-staging-a0d814f5e1ccf2cabe9af71505cb99a908f64a5efb531063253090cf7412\", \"--files-from\", \"/tmp/package-freebsd-build-36dcccb637b7ab270f329f125a8a0fc2650e2ae00778dbb78edb24955b6b1/file_list\", \"--transform\", \"s|^\\\\([^+]\\\\)|/\\\\1|\"]", :level=>:error)

I recognized that the problem is caused by the --transform flag that isn't supported by the default FreeBSD tar.

bsdtar 3.6.0 - libarchive 3.6.0 zlib/1.2.12 liblzma/5.2.5 bz2lib/1.0.8 libzstd/1.4.8

In this MR, I provided a patch that replaces the --transform flag with the `-s' flag that has the same meaning on FreeBSD tar but uses a little different pattern format.

Only workaround I found is to remove the default tar executable and replace it with the gtar (GNU tar), e.g.:

pkg install gtar
mv /usr/bin/tar /usr/bin/bsdtar
mv /usr/local/bin/gtar /usr/bin/tar

But it is an ugly hack and shouldn't be used in a production environment.