net-im/dino: specify valac for build system to use

Before, dino's cmake scripts just searched for unversioned valac, and
versioned ones with versions in the range 0.32 - 0.38.

There are good reasons to let Portage decide which valac to use.

* Now we have 0.40 and 0.42 in Gentoo tree. These are not detected by
  dino build system (bug 678402).
* Allow users to override valac version uniformly across Gentoo with
  VALAC envvar.

Suggested-by: Daniel Kenzelmann <gentoo@k8n.de>
Bug: https://bugs.gentoo.org/678402
Package-Manager: Portage-2.3.51, Repoman-2.3.12
Signed-off-by: Andrey Utkin <andrey_utkin@gentoo.org>

net-im/dino/dino-9999.ebuild

@@ -47,6 +47,7 @@ DEPEND="
 
 src_prepare() {
 	cmake-utils_src_prepare
+	vala_src_prepare
 }
 
 src_configure() {
@@ -57,6 +58,7 @@ src_configure() {
 	)
 	local mycmakeargs+=(
 		"-DDISABLED_PLUGINS=$(local IFS=";"; echo "${disabled_plugins[*]}")"
+		"-DVALA_EXECUTABLE=${VALAC}"
 	)
 
 	if has test ${FEATURES}; then