Hello

I discovered a little problem while trying to build emacs-25 with modules on
OpenBSD-current. The problem is that an assertion fails because
HAVE_ATTRIBUTE_CLEANUP is not true, even though I'm using clang which does
support the cleanup attribute (I think).

This is because the test for whether CC supports that attribute
(m4/ax_gcc_var_attribute.m4 m4/ax_gcc_var_attribute.m4) only checks if there
were warnings issued and if so decides that the compiler has no support. But
OpenBSDs linker (I think it is) outputs the following warnings:

/usr/X11R6/lib/libX11.so.16.1: warning: warning: strcpy() is almost always misused, please use strlcpy()
/usr/X11R6/lib/libX11.so.16.1: warning: warning: strcat() is almost always misused, please use strlcat()
/usr/X11R6/lib/libX11.so.16.1: warning: warning: sprintf() is often misused, please use snprintf()

which are completely unrelated to lack of attribute support.

The attached fix allows me to build. It isn't meant as a real solution,
it's more to illustrate the problem.

I guess another way to go migt be to run this test with empty linker flags, but
I haven't tried that.

Either way, I hope this is of some use.

-- Joakim