Fix gen-embed: set JERBOA_DEV_NATIVE, not JSH_DEV_NATIVE

ober

16a4b679f33160eddec73161d176766937668636

diff --git a/Makefile b/Makefile
index cfe7028..6553c38 100644
--- a/Makefile
+++ b/Makefile
@@ -340,7 +340,7 @@ gen-embed: ensure-jerboa-tools vendor-native-rs-pruned
 		$(MAKE) jerboa-native-host; \
 		JSH_BUILD_ROOT="$(CURDIR)" JSH_EMBED_DIR="$(abspath $(JSH_EMBED))" \
 		JERBOA_NATIVE_LIB="$(abspath $(JERBOA_NATIVE_HOST_LIB))" \
-		JSH_DEV_NATIVE=1 $(JEXEC) gen-embed.ss; \
+		JERBOA_DEV_NATIVE=1 $(JEXEC) gen-embed.ss; \
 	elif [ ! -f src/jsh/embed-data.sls ]; then \
 		echo "=== Generating empty embed-data.sls (batch mode, no TTY) ==="; \
 		mkdir -p src/jsh; \