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 b147846b67)

core/config.mk

@@ -492,7 +492,16 @@ LLVM_RS_CC := $(HOST_OUT_EXECUTABLES)/llvm-rs-cc
 BCC_COMPAT := $(HOST_OUT_EXECUTABLES)/bcc_compat
 DEPMOD := $(HOST_OUT_EXECUTABLES)/depmod
 
+#TODO: use a smaller -Xmx value for most libraries;
+#      only core.jar and framework.jar need a heap this big.
+ifndef DX_ALT_JAR
 DX := $(HOST_OUT_EXECUTABLES)/dx
+DX_COMMAND := $(DX) -JXms16M -JXmx2048M
+else
+DX := $(DX_ALT_JAR)
+DX_COMMAND := java -Xms16M -Xmx2048M -jar $(DX)
+endif
+
 MAINDEXCLASSES := $(HOST_OUT_EXECUTABLES)/mainDexClasses
 
 SOONG_ZIP := $(SOONG_HOST_OUT_EXECUTABLES)/soong_zip

core/definitions.mk

@@ -2546,14 +2546,11 @@ $(hide) java -jar $(DESUGAR) \
 endef
 
 
-#TODO: use a smaller -Xmx value for most libraries;
-#      only core.jar and framework.jar need a heap this big.
 define transform-classes.jar-to-dex
 @echo "target Dex: $(PRIVATE_MODULE)"
 @mkdir -p $(dir $@)
 $(hide) rm -f $(dir $@)classes*.dex
-$(hide) $(DX) \
-    -JXms16M -JXmx2048M \
+$(hide) $(DX_COMMAND) \
     --dex --output=$(dir $@) \
     --min-sdk-version=$(call codename-or-sdk-to-sdk,$(PRIVATE_DEFAULT_APP_TARGET_SDK)) \
     $(if $(NO_OPTIMIZE_DX), \