zip uses C89-only features, so it needs to be built in C89 mode.
diff --git a/unix/Makefile b/unix/Makefile
index 86cf54bf0f56cea9..244390893eab5fc6 100644
--- a/unix/Makefile
+++ b/unix/Makefile
@@ -202,7 +202,7 @@ generic: flags
eval $(MAKE) $(MAKEF) zips `cat flags`
generic_gcc:
- $(MAKE) $(MAKEF) generic CC=gcc CPP="gcc -E"
+ $(MAKE) $(MAKEF) generic CC="gcc -std=gnu89" CPP="gcc -E"
# AT&T 6300 PLUS (don't know yet how to allocate 64K bytes):
att6300nodir: