Two-line fix for "./configure is too sensitive to stray files/subdirectories"

[mkoeppe]

This branch can be merged by people who are working with tickets pre-9.1.beta2 who cannot easily merge current develop into that ticket.

It turns an error issued by configure when they are stray files in build/pkgs (such as the generated files introduced in #29038).

Before this ticket:

$ mkdir -p build/pkgs/xyzzy/foo
$ ./bootstrap && ./configure
...
configure: error: "/Users/mkoeppe/s/sage/sage-rebasing/worktree-algebraic-2018-spring/build/pkgs/xyzzy/type" is missing.

After this ticket:

...
configure: WARNING: "/Users/mkoeppe/s/sage/sage-rebasing/worktree-algebraic-2018-spring/build/pkgs/xyzzy/type" is missing.  Leftovers from another branch?
...

CC: @dimpase @embray @vbraun

Component: build

Author: Matthias Koeppe

Branch/Commit: 171181f

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29120

[mkoeppe]

Branch: u/mkoeppe/one-line-fix-configure-too-sensitive-to-stray-files-in-build-pkgs

[mkoeppe]

Commit: 1f193bf

[mkoeppe]

comment:3

The branch is on top of sage 8.7.

---

New commits:

1f193bf

Issue only a warning, not an error, if there are stray files in build/pkgs

[mkoeppe]

Author: Matthias Koeppe

[dimpase]

Reviewer: Dima Pasechnik

[dimpase]

comment:7

lgtm

[mkoeppe]

comment:8

Thanks!

[sagetrac-git]

Changed commit from 1f193bf to 171181f

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

171181f

fixup

[mkoeppe]

comment:10

Sometimes 2 lines are better than 1.

[dimpase]

comment:12

Could we please avoid continue, by putting the stuff to run fully into then clause?

[mkoeppe]

comment:13

I think it's better if the diff is small.

[dimpase]

comment:14

I don't like this Fortran coding style, but OK :-)

[mkoeppe]

comment:15

Thanks!

[embray]

comment:16

+1 thanks.

[vbraun]

Changed branch from u/mkoeppe/one-line-fix-configure-too-sensitive-to-stray-files-in-build-pkgs to 171181f