Re-compute DX command if it changes for PDK.

Bug 62360631
Tested build of PDK.

Test: builds
Change-Id: I7cbd649a8a3ce4326e513d5a808b76fbb011d99e
Merged-In: I7cbd649a8a3ce4326e513d5a808b76fbb011d99e
(cherry picked from commit af4bde42396b9a770370002d74a2b0658f20d0f1)
diff --git a/core/config.mk b/core/config.mk
index 6ca45c0..aa6ed9b 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -554,6 +554,7 @@
 SIGNAPK_JNI_LIBRARY_PATH := $(prebuilt_sdk_tools)/$(HOST_OS)/lib64
 
 DX := $(prebuilt_sdk_tools)/dx
+DX_COMMAND := $(DX) -JXms16M -JXmx2048M
 MAINDEXCLASSES := $(prebuilt_sdk_tools)/mainDexClasses
 
 # Don't use prebuilts in PDK