[caribou] build: Mark as not supporting srcdir != builddir

[Colin Walters <walters src gnome org>]

commit 9a57b567b4753d948a0c3027d0ff26debd7c7314
Author: Colin Walters <walters verbum org>
Date:   Mon Feb 18 17:20:39 2013 -0500

    build: Mark as not supporting srcdir != builddir
    
    Basically automake's vala rules cd $(srcdir), which breaks variable
    references like $(top_srcdir), since they're relative to the build
    directory.

 configure.ac |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 618af87..57e3253 100644
--- a/configure.ac
+++ b/configure.ac
@@ -14,6 +14,12 @@ AM_MAINTAINER_MODE([enable])
 # to configure or passing V=1 to make
 AM_SILENT_RULES([yes])
 
+dnl http://people.gnome.org/~walters/docs/build-api.txt
+dnl We don't support separate builddir when building from git;
+dnl The automake vala rules run cd srcdir which screws up the
+dnl top_srcdir variable references.
+echo \#buildapi-variable-no-builddir >/dev/null
+
 AM_PATH_GLIB_2_0(2.27.5,,,gobject)
 if test "$GLIB_LIBS" = ""; then
    AC_MSG_ERROR(GLIB 2.27.5 or later is required to build libcaribou)