YJIT: Add `make yjit-smoke-test` [ci skip]

I have this as a shell command and Maxime told me that she finds it
useful, too. I tested this on a release build and a dev build.

Note I intentional didn't put `$(Q)` in front of everything so `make`
echos the command it runs.

yjit/yjit.mk

@@ -86,6 +86,15 @@ update-yjit-bench:
 	$(Q) $(tooldir)/git-refresh -C $(srcdir) --branch main \
 		https://github.com/Shopify/yjit-bench yjit-bench $(GIT_OPTS)
 
+# Gives quick feedback about YJIT. Not a replacement for a full test run.
+.PHONY: yjit-smoke-test
+yjit-smoke-test:
+ifneq ($(strip $(CARGO)),)
+	$(CARGO) test --all-features -q --manifest-path='$(top_srcdir)/yjit/Cargo.toml'
+endif
+	$(MAKE) btest RUN_OPTS='--yjit-call-threshold=1' BTESTS=-j
+	$(MAKE) test-all TESTS='$(top_srcdir)/test/ruby/test_yjit.rb'
+
 # Generate Rust bindings. See source for details.
 # Needs `./configure --enable-yjit=dev` and Clang.
 ifneq ($(strip $(CARGO)),) # if configure found Cargo