setup fliplink

.cargo/config.toml

@@ -1,6 +1,10 @@
 [target.'cfg(all(target_arch = "arm", target_os = "none"))']
 runner = "probe-rs run --chip STM32F411VETx"
 
+# flip-link: zero-cost stack-overflow protection. It wraps the real linker
+# (LLD here), so it stays compatible with the -Tlink.x / -Tdefmt.x args below.
+linker = "flip-link"
+
 rustflags = [
   # LLD (shipped with the Rust toolchain) is used as the default linker
   "-C", "link-arg=-Tlink.x",