Enable goma in soong

Pass the USE_GOMA flag to soong, and export the CC_WRAPPER environment
variable after adding gomacc to it.

Bug: 31142427
Change-Id: I6de698a40817c0615b03fa17bd27075465d79ffd
diff --git a/core/config.mk b/core/config.mk
index fb05897..a2d5e3f 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -284,6 +284,9 @@
 include $(BUILD_SYSTEM)/ccache.mk
 include $(BUILD_SYSTEM)/goma.mk
 
+export CC_WRAPPER
+export CXX_WRAPPER
+
 ifdef TARGET_PREFER_32_BIT
 TARGET_PREFER_32_BIT_APPS := true
 TARGET_PREFER_32_BIT_EXECUTABLES := true