Put the implicit memory.x behind a memory_x feature on embassy-stm32.

stm32-metapac/Cargo.toml

@@ -17,6 +17,7 @@ regex = "1.5.4"
 
 [features]
 rt = ["cortex-m-rt/device"]
+memory_x = []
 
 # BEGIN GENERATED FEATURES
 # Generated by gen_features.py. DO NOT EDIT.

stm32-metapac/build.rs

@@ -27,5 +27,13 @@ fn main() {
         out_dir.display(),
         chip_name.to_ascii_lowercase()
     );
+
+    #[cfg(feature = "memory_x")]
+    println!(
+        "cargo:rustc-link-search={}/src/chips/{}/memory_x/",
+        out_dir.display(),
+        chip_name.to_ascii_lowercase()
+    );
+
     println!("cargo:rerun-if-changed=build.rs");
 }