ICU-20945 Making icudt66.dll for x64 as PE32+
diff --git a/icu4c/source/data/makedata.mak b/icu4c/source/data/makedata.mak
index 2a53528..4655ff6 100644
--- a/icu4c/source/data/makedata.mak
+++ b/icu4c/source/data/makedata.mak
@@ -214,6 +214,9 @@
 !IF "$(UWP)" == "UWP"
 COMMON_ICUDATA_ARGUMENTS=$(COMMON_ICUDATA_ARGUMENTS) -u
 !ENDIF
+!IF "$(CFG)" == "x64\Release" || "$(CFG)" == "x64\Debug"
+COMMON_ICUDATA_ARGUMENTS=$(COMMON_ICUDATA_ARGUMENTS) -a X64
+!ENDIF
 !IF "$(CFG)" == "ARM\Release" || "$(CFG)" == "ARM\Debug"
 COMMON_ICUDATA_ARGUMENTS=$(COMMON_ICUDATA_ARGUMENTS) -a ARM
 !ENDIF