Assumes GNU cp is in path; a bug should be filed upstream to not use

GNU-specific flags or configure should detect GNU cp and require it.

Patch itself is not appropriate for upstream.

XXX file upstream bug

--- p11-kit-0.23.1/build/gtk-doc.make 2014-11-12 02:58:50.000000000 -0800

+++ p11-kit-0.23.1/build/gtk-doc.make 2015-05-27 14:23:15.544773257 -0700

@@ -82,7 +82,7 @@

if test "x$$files" != "x" ; then \

for file in $$files ; do \

test -f $(abs_srcdir)/$$file && \

- cp -pu $(abs_srcdir)/$$file $(abs_builddir)/ || true; \

+ gcp -pu $(abs_srcdir)/$$file $(abs_builddir)/ || true; \

done; \

fi; \

fi