webkit_gtk: Use ninja instead of make.

Let's see if this fixes out-of-memory problems on the buildmaster...

net-libs/webkit-gtk/webkit_gtk-2.38.2.recipe

@@ -160,6 +160,7 @@ BUILD_PREREQUIRES="
 	cmd:gcc$secondaryArchSuffix
 	cmd:gperf
 	cmd:make
+	cmd:ninja
 	cmd:orcc$secondaryArchSuffix
 	cmd:perl
 	cmd:pkg_config$secondaryArchSuffix
@@ -179,7 +180,7 @@ BUILD()
 {
 	export DISABLE_ASLR=1
 
-	cmake -S. -Bbuild \
+	cmake -S. -Bbuild -GNinja \
 		-DCMAKE_BUILD_TYPE=Release \
  		-DCMAKE_CXX_FLAGS="-D_BSD_SOURCE" \
 		-DPORT=GTK \
@@ -231,7 +232,7 @@ BUILD()
 		-DUSE_WPE_RENDERER=OFF \
 		$cmakeDirArgs
 
-	make -C build -j4
+	ninja -C build
 }
 
 INSTALL()