add make demos to CI

Author: bradjc

.github/workflows/ci.yml

@@ -46,3 +46,4 @@ jobs:
           echo 'rustflags = ["-D", "warnings"]' >> .cargo/config.toml
           make -j2 setup
           make -j2 test
+          make demos

Makefile

@@ -242,6 +242,11 @@ $(eval $(call platform_build,msp432,thumbv7em-none-eabi))
 $(eval $(call platform_build,clue_nrf52840,thumbv7em-none-eabi))
 $(eval $(call platform_flash,clue_nrf52840,thumbv7em-none-eabi))
 
+.PHONY: demos
+demos:
+	$(MAKE) -C demos/embedded_graphics/spin
+	$(MAKE) -C demos/embedded_graphics/buttons
+
 # clean cannot safely be invoked concurrently with other actions, so we don't
 # need to depend on toolchain. We also manually remove the nightly toolchain's
 # target directory, in case the user doesn't want to install the nightly