use fallback implementation in Miri

Author: RalfJung

build.rs

@@ -39,6 +39,10 @@ fn enable_simd(/*version: Version*/) {
         println!("cargo:warning=building for no_std disables httparse SIMD");
         return;
     }
+    if env::var_os("CARGO_CFG_MIRI").is_some() {
+        println!("cargo:warning=building for Miri disables httparse SIMD");
+        return;
+    }
 
     let env_disable = "CARGO_CFG_HTTPARSE_DISABLE_SIMD";
     if var_is(env_disable, "1") {