.gitignore file has 'Makefile.in' rule that matches files/Makefile.in . But files/Makefile.in is necessary for building so I think rule that makes exception for files/Makefile.in should be added.
@vovka-korovka Should I change it into ./Makefile.in ?
You just should apply follow simple change for .gitignore file
diff --git a/.gitignore b/.gitignore
index fa5927a..44680f8 100644
@@ -1,5 +1,6 @@
@vovka-korovka Normally I would have asked you to make a pull request, but now I'll commit it myself since it may have to be done quickly to get into 1.6 series.
Sorry, will create pull requests in future.
Thanks for your help anyway.