Add -mno-outline-atomics when building C code

Fixes building the aarch64 toolchain. Disables emitting
`__aarch64_swp4_sync` and similar functions.

build.rs

@@ -59,6 +59,7 @@ fn main() {
         .flag("-nostdlib")
         .include(&format!("{}/include", crate_dir))
         .include(&format!("{}/target/include", crate_dir))
+        .flag("-mno-outline-atomics")
         .flag("-fno-stack-protector")
         .flag("-Wno-expansion-to-defined")
         .files(