[latexila] build: fix out-of-source-dir building

[Sébastien Wilmet <swilmet src gnome org>]

commit 7b5dacb591dc804e54d5b2142921e23e88b9e084
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sat Dec 16 13:00:15 2017 +0100

    build: fix out-of-source-dir building
    
    Add vapidir with absolute folder-path to just built latexila.vapi.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=791680

 src/Makefile.am |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index e6b89ab..5119dd7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -4,16 +4,17 @@ bin_PROGRAMS = latexila
 
 # --disable-since-check is used because LaTeXila often depends on unstable
 # versions of GNOME libraries.
-AM_VALAFLAGS =                 \
-       --disable-since-check   \
-       --pkg gtk+-3.0          \
-       --pkg gtksourceview-4   \
-       --pkg Tepl-4            \
-       --pkg gspell-1          \
-       --pkg gee-0.8           \
-       --pkg posix             \
-       --target-glib=2.50      \
-       --vapidir liblatexila   \
+AM_VALAFLAGS =                                 \
+       --disable-since-check                   \
+       --pkg gtk+-3.0                          \
+       --pkg gtksourceview-4                   \
+       --pkg Tepl-4                            \
+       --pkg gspell-1                          \
+       --pkg gee-0.8                           \
+       --pkg posix                             \
+       --target-glib=2.50                      \
+       --vapidir liblatexila                   \
+       --vapidir $(abs_builddir)/liblatexila   \
        --pkg latexila
 
 # The valac command is always executed in the sources directory, not the build