Sometimes we need to patch a file that is a dependency for some other
automatically generated file that comes in a release tarball. As a
result, make tries to regenerate the dependent file using additional
tools (e.g. help2man), which would not be needed otherwise.
In some cases, it's preferable to avoid that (e.g. see #21255). A way
to do that is to save the modification timestamps before patching and
restoring them afterwards. This PR introduces a context wrapper that
does that.
4d7a9df810