release: force xz compression for Debian package

The GCM Debian package currently fails to install on Debian with the
following error:

error: archive 'gcm-linux_amd64.2.0.886.deb' uses unknown compression for
member 'control.tar.zst', giving up

It appears that the version of dpkg that ships with Debian does not
support zstd compression [1]. Enforcing xz compression resolves the issue.

This also provides an opportunity to clean up some unused variables in
pack.sh and ensure we check the architecture is found before attempting to
use the ARCH variable.

[1]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=892664

Author: Lessley Dennington

src/linux/Packaging.Linux/pack.sh

@@ -12,10 +12,6 @@ OUT="$ROOT/out"
 PROJ_OUT="$OUT/linux/Packaging.Linux"
 INSTALLER_SRC="$SRC/osx/Installer.Mac"
 
-# Product information
-IDENTIFIER="com.microsoft.gitcredentialmanager"
-INSTALL_LOCATION="/usr/local/share/gcm-core"
-
 # Parse script arguments
 for i in "$@"
 do
@@ -51,6 +47,10 @@ fi
 
 ARCH="`dpkg-architecture -q DEB_HOST_ARCH`"
 
+if test -z "$ARCH"; then
+    die "Could not determine host architecture!"
+fi
+
 TAROUT="$PROJ_OUT/$CONFIGURATION/tar/"
 TARBALL="$TAROUT/gcm-linux_$ARCH.$VERSION.tar.gz"
 SYMTARBALL="$TAROUT/gcm-linux_$ARCH.$VERSION-symbols.tar.gz"
@@ -60,10 +60,6 @@ DEBROOT="$DEBOUT/root"
 DEBPKG="$DEBOUT/gcm-linux_$ARCH.$VERSION.deb"
 mkdir -p "$DEBROOT"
 
-if test -z "$ARCH"; then
-    die "Could not determine host architecture!"
-fi
-
 # Set full read, write, execute permissions for owner and just read and execute permissions for group and other
 echo "Setting file permissions..."
 /bin/chmod -R 755 "$PAYLOAD" || exit 1
@@ -114,8 +110,6 @@ Description: Cross Platform Git Credential Manager command line utility.
  For more information see https://aka.ms/gcm
 EOF
 
-mkdir -p "$INSTALL_TO" "$LINK_TO"
-
 # Copy all binaries and shared libraries to target installation location
 cp -R "$PAYLOAD"/* "$INSTALL_TO" || exit 1
 
@@ -131,6 +125,6 @@ if [ ! -f "$LINK_TO/git-credential-manager-core" ]; then
         "$LINK_TO/git-credential-manager-core" || exit 1
 fi
 
-dpkg-deb --build "$DEBROOT" "$DEBPKG" || exit 1
+dpkg-deb -Zxz --build "$DEBROOT" "$DEBPKG" || exit 1
 
 echo $MESSAGE