[rygel] build: Make missing gtk-doc non-fatal

[Jens Georg <jensgeorg src gnome org>]

commit 964ab57cff99bc53b0ccd6a9d01efaeadc93216b
Author: Jens Georg <jensg openismus com>
Date:   Sun Sep 29 12:30:59 2013 +0200

    build: Make missing gtk-doc non-fatal
    
    Only fail if gtk-doc is missing when doc generation was requested explicitly
    via --enable-valadoc
    
    https://bugzilla.gnome.org/show_bug.cgi?id=692509

 configure.ac |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 64b9a60..04ff924 100644
--- a/configure.ac
+++ b/configure.ac
@@ -361,7 +361,7 @@ dnl This is on by default when using autogen.sh
 dnl (so it is not on by default when building from a tarball with configure.)
 AC_ARG_ENABLE(valadoc,
   AS_HELP_STRING([--enable-valadoc[=@<:@no/auto/yes@:>@]], [Enable valadoc support]),,
-    [enable_valadoc=no])
+    [enable_valadoc=auto])
 
 found_valadoc=no
 AS_IF([test "x$enable_valadoc" != "xno"], [
@@ -369,7 +369,11 @@ AS_IF([test "x$enable_valadoc" != "xno"], [
     AS_IF([test -x "$VALADOC"], [
       found_valadoc=yes
       AC_SUBST(VALADOC)
-      PKG_CHECK_MODULES([GTKDOC],[gtk-doc >= 1.0])
+      PKG_CHECK_MODULES([GTKDOC],[gtk-doc >= 1.0],,
+                        AS_IF([test "x$enable_valadoc" == "xyes"],
+                              [AC_MSG_ERROR([Unable to find gtk-doc])],
+                              [found_valadoc=no])
+                        )
     ], [
       AS_IF([test "x$enable_valadoc" == "xyes"], AC_MSG_ERROR([Unable to find valadoc]))
     ])