jack: Use TERMUX_DX variable

disabled-packages/javac/build.sh

@@ -11,7 +11,7 @@ termux_step_make () {
 	RAW_JAR=/usr/lib/jvm/java-7-openjdk-amd64/lib/tools.jar
 
         mkdir -p $TERMUX_PREFIX/share/dex
-	$ANDROID_HOME/build-tools/$TERMUX_ANDROID_BUILD_TOOLS_VERSION/dx \
+	$TERMUX_DX \
 		--dex \
 		--output=$TERMUX_PREFIX/share/dex/tools.jar \
 		$RAW_JAR

packages/jack/build.sh

@@ -13,7 +13,7 @@ termux_step_make () {
 
 	# Create $USR/share/dex for dex files, and $USR/share/jack for .jack library files produced by jill:
         mkdir -p $TERMUX_PREFIX/share/{dex,jack}
-	$ANDROID_HOME/build-tools/$TERMUX_ANDROID_BUILD_TOOLS_VERSION/dx \
+	$TERMUX_DX \
 		--dex \
 		--output=$TERMUX_PREFIX/share/dex/jack.jar \
 		$JACK_JAR