Use pkgbuild's --install-location flag when fpm's --prefix is given.

[jordansissel]

A user reported that on macOS Catalina, the default pkgbuild install
location may result in a .pkg file which cannot be installed.

This change makes fpm's --prefix option pass through to pkgbuild's
--install-location flag

With macOS Catalina, you can no longer store files or data in the read-only system volume, nor can you write to the "root" directory ( / ) from the command line, such as with Terminal.

References:

• macOS Catalina's new read-only root filesystem: https://support.apple.com/en-us/HT210650

Fixes #1908

[jordansissel]

I don't have a macOS Catalina machine to test with, so I'll have to test and hope I'm doing it right from Linux.

On my linux machine, I faked it by making a pkgbuild executable that just prints the arguments:

#!/bin/sh

echo ">>" "$0" "$@"

Testing fpm defaults (no given --prefix flag), and trying to print just the command-line arguments. In this example, no --install-location flag should be present because fpm's --prefix flag is not set:

% bundle exec bin/fpm --debug -s empty -t osxpkg -n example | grep pkgbuild | fex '0,/:message/"2'
Running command
>> /home/jls/bin/pkgbuild --identifier example --info /tmp/fpm-PackageInfo20220603-19372-k5evbs --version 1.0 --ownership recommended --root /tmp/package-osxpkg-staging-d37efd5a5a3e5e9ee4ad96c580fea275f8e865fa250570073465f86771d0 example-1.0.pkg

Now, if I specify --prefix /Applications/example, fpm should include --install-location when invoking pkgbuild:

% bundle exec bin/fpm --debug -s empty -t osxpkg -n example --prefix /Applications/example | grep pkgbuild | fex '0,/:message/"2'
Running command
>> /home/jls/bin/pkgbuild --identifier example --info /tmp/fpm-PackageInfo20220603-19385-ahzws5 --version 1.0 --ownership recommended --root /tmp/package-osxpkg-staging-004778ce9aea5b2f40a4e5b12d08db76656aeb5b6c71da49ae1d714a5f1e --install-location /Applications/example example-1.0.pkg

(Github makes pre-formatted things scrollable horizontally, so you might have to scroll to the right on the above examples.

Based on this testing, I think this change should work, roughly summarizing:

• Without --prefix: pkgbuild ... example-1.0.pkg (no use of --install-location)
• With --prefix /Applications/example given: pkgbuild ... --install-location /Applications/example example-1.0.pkg