ICU-20859 ICU4C: Python data build uses wrong value for tool_cfg
diff --git a/icu4c/source/data/makedata.mak b/icu4c/source/data/makedata.mak
index 951f76f..5bf3619 100644
--- a/icu4c/source/data/makedata.mak
+++ b/icu4c/source/data/makedata.mak
@@ -270,7 +270,7 @@
 		--mode windows-exec \
 		--src_dir "$(ICUSRCDATA)" \
 		--tool_dir "$(ICUTOOLS)" \
-		--tool_cfg "$(CFG)" \
+		--tool_cfg "$(CFGTOOLS)" \
 		--out_dir "$(ICUBLD_PKG)" \
 		--tmp_dir "$(ICUTMP)" \
 		--filter_file "$(ICU_DATA_FILTER_FILE)" \