Don't double-wrap with gomacc

config.mk is parsed by make and then kati, and goma.mk appends to
CC_WRAPPER.  Only export it from make so gomacc doesn't appear twice on
the command line.

Bug: 31142427
Change-Id: I5ad97ee3a00b013faa620215c839499b48528e00
diff --git a/core/config.mk b/core/config.mk
index a2d5e3f..c04e660 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -281,11 +281,13 @@
 include $(BUILD_SYSTEM)/combo/select.mk
 endif
 
+ifndef KATI
 include $(BUILD_SYSTEM)/ccache.mk
 include $(BUILD_SYSTEM)/goma.mk
 
 export CC_WRAPPER
 export CXX_WRAPPER
+endif
 
 ifdef TARGET_PREFER_32_BIT
 TARGET_PREFER_32_BIT_APPS := true