build: fix semantic ver generation for windows

Fix syntax error when generating semantic versions on windows hosts.

Change-Id: Idba8827145b829a8ba07ff0540407dbfa1ca7984
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
diff --git a/make_helpers/windows.mk b/make_helpers/windows.mk
index 0f78f61..d95d7ee 100644
--- a/make_helpers/windows.mk
+++ b/make_helpers/windows.mk
@@ -81,9 +81,9 @@
 # by defining the MAKE_BUILD_STRINGS macro.
 BUILT_TIME_DATE_STRING = const char build_message[] = "Built : "${BUILD_MESSAGE_TIMESTAMP};
 VERSION_STRING_MESSAGE = const char version_string[] = "${VERSION_STRING}";
-const char version[] = "${VERSION}";
+VERSION_MESSAGE = const char version[] = "${VERSION}";
 define MAKE_BUILD_STRINGS
-	@echo $$(BUILT_TIME_DATE_STRING) $$(VERSION_STRING_MESSAGE) | \
+	@echo $$(BUILT_TIME_DATE_STRING) $$(VERSION_STRING_MESSAGE) $$((VERSION_MESSAGE)) | \
 		$$(CC) $$(TF_CFLAGS) $$(CFLAGS) -x c -c - -o $1
 endef