Add a desugar step between javac and proguard

This enables support for lambdas by passing class files through the
desugar tool.

Test: m -j checkbuild tests cts
Change-Id: I14ec152355243fd67fe2f107ccbe67a1b4e7e262
diff --git a/core/config.mk b/core/config.mk
index 9c926dd..a6981e0 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -603,6 +603,7 @@
 MKTARBALL := build/tools/mktarball.sh
 TUNE2FS := $(HOST_OUT_EXECUTABLES)/tune2fs$(HOST_EXECUTABLE_SUFFIX)
 JARJAR := $(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
+DESUGAR := $(HOST_OUT_JAVA_LIBRARIES)/desugar.jar
 DATA_BINDING_COMPILER := $(HOST_OUT_JAVA_LIBRARIES)/databinding-compiler.jar
 FAT16COPY := build/tools/fat16copy.py
 CHECK_LINK_TYPE := build/tools/check_link_type.py