[gcc(refs/vendors/redhat/heads/gcc-8-branch)] Fix various limitations of git-backport.py.

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:ad37325f42d79e6e09a3cd91592bbd0083aa0c4a

commit ad37325f42d79e6e09a3cd91592bbd0083aa0c4a
Author: Martin Liska <mliska@suse.cz>
Date:   Fri May 29 11:29:25 2020 +0200

    Fix various limitations of git-backport.py.
    
    I've just tested the script and I'm going to install the patch
    to all active branches.
    
    contrib/ChangeLog:
    
            * git-backport.py: The script did 'git co HEAD~' when
            there was no modified ChangeLog file in a successful
            git cherry pick.
            Run cherry-pick --continue without editor.
    
    (cherry picked from commit 24663f1f6d709daf8913484914ed01af9f7a480a)

Diff:
---
 contrib/git-backport.py | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/contrib/git-backport.py b/contrib/git-backport.py
index 6a115c34d40..3a9413dcd27 100755
--- a/contrib/git-backport.py
+++ b/contrib/git-backport.py
@@ -30,9 +30,13 @@ if __name__ == '__main__':
 
     r = subprocess.run('git cherry-pick -x %s' % args.revision, shell=True)
     if r.returncode == 0:
-        cmd = 'git show --name-only --pretty="" -- "*ChangeLog" |' \
-              'xargs git checkout HEAD~'
-        subprocess.check_output(cmd, shell=True)
+        cmd = 'git show --name-only --pretty="" -- "*ChangeLog"'
+        changelogs = subprocess.check_output(cmd, shell=True, encoding='utf8')
+        changelogs = changelogs.strip()
+        if changelogs:
+            for changelog in changelogs.split('\n'):
+                subprocess.check_output('git checkout HEAD~ %s' % changelog,
+                                        shell=True)
         subprocess.check_output('git commit --amend --no-edit', shell=True)
     else:
         # 1) remove all ChangeLog files from conflicts
@@ -55,6 +59,7 @@ if __name__ == '__main__':
 
         # try to continue
         if len(conflicts) == len(changelogs):
-            subprocess.check_output('git cherry-pick --continue', shell=True)
+            cmd = 'git -c core.editor=true cherry-pick --continue'
+            subprocess.check_output(cmd, shell=True)
         else:
             print('Please resolve all remaining file conflicts.')