Use 'cp' instead of 'cp -av' to fix portable issue

Neither '-a' nor '-v' of 'cp' is available on OpenBSD 5.3, so use 'cp'
instead to fix portable issue.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=69789Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

autogen.sh

@@ -15,7 +15,7 @@ DIE=0
 
 if [ -f .git/hooks/pre-commit.sample -a ! -f .git/hooks/pre-commit ] ; then
     echo "Activating pre-commit hook."
-    cp -av .git/hooks/pre-commit.sample .git/hooks/pre-commit
+    cp .git/hooks/pre-commit.sample .git/hooks/pre-commit
     chmod +x .git/hooks/pre-commit
 fi