[cairo] --enable-gtk-doc fix

[Russell Shaw]

Regardless of whether --enable-gtk-doc is done at configure time,
gtk-doc (the stuff in cairo/doc/public) is always enabled. This fixes
that:

--- cairo-old/doc/Makefile.am   2005-01-28 06:35:26.000000000 +1100
+++ cairo/doc/Makefile.am       2005-08-15 11:38:11.000000000 +1000
@@ -1,2 +1,4 @@
+if ENABLE_GTK_DOC
  SUBDIRS=public
+endif


The next patch enables cairo.devhelp to get rebuilt whenever a .c
file changes, when you run make from the top level or within the
doc/public directory. Previously, cairo.devhelp would not be built
no matter where make was run from.

Don't know the precise effect of the first half, but it looked
like a similar problem.

diff -u  gtk-doc.make  gtk-doc.make-new
--- gtk-doc.make        2005-08-14 13:11:04.000000000 +1000
+++ gtk-doc.make-new    2005-08-14 13:11:52.000000000 +1000
@@ -72,7 +72,7 @@
         touch tmpl-build.stamp

  tmpl.stamp: tmpl-build.stamp
-       @true
+       touch tmpl.stamp

  #### xml ####

@@ -84,7 +84,7 @@
         touch sgml-build.stamp

  sgml.stamp: sgml-build.stamp
-       @true
+       touch sgml.stamp

  #### html ####