Allows DX alternative Jar.

Test: m -j20 ANDROID_COMPILE_WITH_JACK=false DX_ALT_JAR=/mnt/m02/dx_alt.jar

Change-Id: I6163280101ff973bc8202a82d2fed42cf0ce6209
(cherry picked from commit b147846b67b18e40f555c79befe143e8eda6e4cf)
2 files changed