Dpkg::Source::Patch: Pass PATCH_GET envvar instead of -g0 to patch

For GNU patch the default value for -g is already 0, but that option is
not available in other systems, such as FreeBSD. Let's switch to use the
environment variable PATCH_GET, so that we make sure it gets set to a
known value, and so that we can stop using the unportable option.

debian/changelog

@@ -82,6 +82,9 @@ dpkg (1.18.0) UNRELEASED; urgency=low
       clarify what whitespace really maps to, we should really match the GnuPG
       implementation anyway, as that's what we use to verify the signatures.
       Reported by Jann Horn <jann@thejh.net>. Fixes CVE-2015-0840.
+    - Pass PATCH_GET environment varialbe instead of -g0 to the patch command
+      in Dpkg::Source::Patch. This allows using non-GNU patch programs, like
+      FreeBSD's patch.
   * Test suite:
     - Check perl code compilation, warnings and strictness.
     - Fix dpkg-divert unit test to work on BSD «rm -rf» that cannot traverse

scripts/Dpkg/Source/Patch.pm

@@ -565,7 +565,7 @@ sub apply {
     $opts{remove_backup} //= 1;
     $opts{create_dirs} //= 1;
     $opts{options} ||= [ '-t', '-F', '0', '-N', '-p1', '-u',
-            '-V', 'never', '-g0', '-b', '-z', '.dpkg-orig'];
+            '-V', 'never', '-b', '-z', '.dpkg-orig'];
     $opts{add_options} //= [];
     push @{$opts{options}}, @{$opts{add_options}};
     # Check the diff and create missing directories
@@ -577,7 +577,7 @@ sub apply {
     spawn(
 	exec => [ 'patch', @{$opts{options}} ],
 	chdir => $destdir,
-	env => { LC_ALL => 'C', LANG => 'C' },
+	env => { LC_ALL => 'C', LANG => 'C', PATCH_GET => '0' },
 	delete_env => [ 'POSIXLY_CORRECT' ], # ensure expected patch behaviour
 	wait_child => 1,
 	nocheck => 1,
@@ -616,7 +616,7 @@ sub check_apply {
     # Set default values to options
     $opts{create_dirs} //= 1;
     $opts{options} ||= [ '--dry-run', '-s', '-t', '-F', '0', '-N', '-p1', '-u',
-            '-V', 'never', '-g0', '-b', '-z', '.dpkg-orig'];
+            '-V', 'never', '-b', '-z', '.dpkg-orig'];
     $opts{add_options} //= [];
     push @{$opts{options}}, @{$opts{add_options}};
     # Check the diff and create missing directories
@@ -627,7 +627,7 @@ sub check_apply {
     my $patch_pid = spawn(
 	exec => [ 'patch', @{$opts{options}} ],
 	chdir => $destdir,
-	env => { LC_ALL => 'C', LANG => 'C' },
+	env => { LC_ALL => 'C', LANG => 'C', PATCH_GET => '0' },
 	delete_env => [ 'POSIXLY_CORRECT' ], # ensure expected patch behaviour
 	from_handle => $self->get_filehandle(),
 	to_file => '/dev/null',

scripts/Dpkg/Source/Quilt.pm

@@ -179,7 +179,7 @@ sub push {
                     verbose => $opts{verbose},
                     force_timestamp => 1, create_dirs => 1, remove_backup => 0,
                     options => [ '-t', '-F', '0', '-N', '-p1', '-u',
-                                 '-V', 'never', '-g0', '-E', '-b',
+                                 '-V', 'never', '-E', '-b',
                                  '-B', ".pc/$patch/", '--reject-file=-' ]);
     };
     if ($@) {
@@ -216,7 +216,7 @@ sub pop {
         $obj->apply($self->{dir}, timestamp => $opts{timestamp},
                     verbose => 0, force_timestamp => 1, remove_backup => 0,
                     options => [ '-R', '-t', '-N', '-p1',
-                                 '-u', '-V', 'never', '-g0', '-E',
+                                 '-u', '-V', 'never', '-E',
                                  '--no-backup-if-mismatch' ]);
     }