libvpx: pass CONFIG_SPATIAL_SVC=yes, configure with --enable-vp9 (#2596)

to add develop/headers/vpx/svc_context.h to the devel package.

media-libs/libvpx/libvpx-1.7.0.recipe

@@ -11,7 +11,7 @@ COPYRIGHT="2009-2012 Google Inc.,
 	The Mozilla Foundation and
 	The Xiph.Org Foundation"
 LICENSE="BSD (3-clause)"
-REVISION="2"
+REVISION="3"
 SOURCE_URI="https://github.com/webmproject/libvpx/archive/v$portVersion.tar.gz"
 CHECKSUM_SHA256="1fec931eb5c94279ad219a5b6e0202358e94a93a90cfb1603578c326abfc1238"
 SOURCE_FILENAME="libvpx-$portVersion.tar.gz"
@@ -85,6 +85,7 @@ BUILD_PREREQUIRES="
 
 BUILD()
 {
+	export CONFIG_SPATIAL_SVC=yes
 	# not an auto tools configure
 	./configure \
 		--prefix="$prefix" \
@@ -92,12 +93,15 @@ BUILD()
 		--as=yasm \
 		--enable-pic \
 		--enable-shared \
-		--enable-vp8
+		--enable-vp8 \
+		--enable-vp9 \
+
 	make $jobArgs
 }
 
 INSTALL()
 {
+	CONFIG_SPATIAL_SVC=yes \
 	make install
 
 	prepareInstalledDevelLibs libvpx