Adjust test to ignore gzip 1.8+ warnings.

--- automake-1.15/t/distcheck-no-prefix-or-srcdir-override.sh	2016-06-14 00:36:26.554218552 +0200
+++ automake-1.15/t/distcheck-no-prefix-or-srcdir-override.sh	2016-06-14 00:37:52.903157770 +0200
@@ -49,7 +49,11 @@ grep "cannot find sources.* in foobar" s
 
 ./configure
 run_make -E -O distcheck
-test ! -s stderr
+
+# Gzip 1.8+ emits warnings like "gzip: warning: GZIP environment
+# variable is deprecated"; filter them out.
+test `grep -v '^gzip: warning' stderr | wc -l` -eq 0
+
 # Sanity check: the flags have been actually seen.
 $PERL -e 'undef $/; $_ = <>; s/ \\\n/ /g; print;' <stdout >t
 grep '/configure .* --srcdir am-src'   t || exit 99
='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=391097782311c82c04b171db7373a0bbfc1d8653'>refs</a><a class='active' href='/guix/log/gnu/services/sddm.scm'>log</a><a href='/guix/tree/gnu/services/sddm.scm?id=391097782311c82c04b171db7373a0bbfc1d8653'>tree</a><a href='/guix/commit/gnu/services/sddm.scm?id=391097782311c82c04b171db7373a0bbfc1d8653'>commit</a><a href='/guix/diff/gnu/services/sddm.scm?id=391097782311c82c04b171db7373a0bbfc1d8653'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/sddm.scm'>
<input type='hidden' name='id' value='391097782311c82c04b171db7373a0bbfc1d8653'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=391097782311c82c04b171db7373a0bbfc1d8653'>root</a>/<a href='/guix/log/gnu?id=391097782311c82c04b171db7373a0bbfc1d8653'>gnu</a>/<a href='/guix/log/gnu/services?id=391097782311c82c04b171db7373a0bbfc1d8653'>services</a>/<a href='/guix/log/gnu/services/sddm.scm?id=391097782311c82c04b171db7373a0bbfc1d8653'>sddm.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/services/sddm.scm?id=391097782311c82c04b171db7373a0bbfc1d8653&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>