Implement x86 chkstk in "rust"

library/compiler-builtins/src/lib.rs

@@ -51,6 +51,9 @@ pub mod mem;
 #[cfg(target_arch = "arm")]
 pub mod arm;
 
+#[cfg(target_arch = "x86")]
+pub mod x86;
+
 #[cfg(target_arch = "x86_64")]
 pub mod x86_64;