msubprojects: Abort the rebase if there's conflicts

Don't leave the subproject tree in a broken / conflicting state. The
user is most likely not a git expert who will know what magic command
to run to fix their source tree.

Author: nirbheek

mesonbuild/msubprojects.py

@@ -229,7 +229,9 @@ def git_rebase(self, revision: str) -> bool:
         try:
             self.git_output(['-c', 'rebase.autoStash=true', 'rebase', 'FETCH_HEAD'])
         except GitException as e:
-            self.log('  -> Could not rebase', mlog.bold(self.repo_dir), 'onto', mlog.bold(revision))
+            self.git_output(['-c', 'rebase.autoStash=true', 'rebase', '--abort'])
+            self.log('  -> Could not rebase', mlog.bold(self.repo_dir), 'onto', mlog.bold(revision),
+                     '-- aborted')
             self.log(mlog.red(e.output))
             self.log(mlog.red(str(e)))
             return False