Fix make install without write privilege to the source directory

by not using a temp file in there for irssi-version.h.
Note that this will still not work if the source has changed
since it was compiled, but that is to be expected.


git-svn-id: file:///var/www/svn.irssi.org/SVN/irssi/trunk@5062 dbcabf3a-b0e7-0310-adc4-f8d773084564

Makefile.am

@@ -10,9 +10,7 @@ default-config.h: $(srcdir)/irssi.conf
 default-theme.h: $(srcdir)/default.theme
 	$(srcdir)/file2header.sh $(srcdir)/default.theme default_theme > default-theme.h
 irssi-version.h:
-	$(srcdir)/irssi-version.sh $(srcdir) > $@.tmp
-	cmp -s $@.tmp $@ || mv $@.tmp $@
-	rm -f $@.tmp
+	$(srcdir)/irssi-version.sh $(srcdir) | cmp -s - $@ || $(srcdir)/irssi-version.sh $(srcdir) >$@
 
 SUBDIRS = src docs scripts