Remove build.rs, use target_has_atomic instead

`target_has_atomic` has been stable since rust 1.60

schemars/Cargo.toml

@@ -10,7 +10,6 @@ license = "MIT"
 readme = "README.md"
 keywords = ["rust", "json-schema", "serde"]
 categories = ["encoding"]
-build = "build.rs"
 rust-version = "1.60"
 
 [dependencies]

schemars/build.rs

@@ -1,25 +0,0 @@
-use std::env;
-
-// Based on https://github.com/serde-rs/serde/blob/master/serde/build.rs
-
-fn main() {
-    let target = env::var("TARGET").unwrap();
-    let emscripten = target == "asmjs-unknown-emscripten" || target == "wasm32-unknown-emscripten";
-
-    // Whitelist of archs that support std::sync::atomic module. Ideally we
-    // would use #[cfg(target_has_atomic = "...")] but it is not stable yet.
-    // Instead this is based on rustc's src/librustc_target/spec/*.rs.
-    let has_atomic64 = target.starts_with("x86_64")
-        || target.starts_with("i686")
-        || target.starts_with("aarch64")
-        || target.starts_with("powerpc64")
-        || target.starts_with("sparc64")
-        || target.starts_with("mips64el");
-    let has_atomic32 = has_atomic64 || emscripten;
-    if has_atomic64 {
-        println!("cargo:rustc-cfg=std_atomic64");
-    }
-    if has_atomic32 {
-        println!("cargo:rustc-cfg=std_atomic");
-    }
-}

schemars/src/json_schema_impls/atomic.rs

@@ -1,19 +1,36 @@
 use std::sync::atomic::*;
 
+#[cfg(target_has_atomic = "8")]
 forward_impl!(AtomicBool => bool);
 
+#[cfg(target_has_atomic = "8")]
 forward_impl!(AtomicI8 => i8);
+
+#[cfg(target_has_atomic = "16")]
 forward_impl!(AtomicI16 => i16);
+
+#[cfg(target_has_atomic = "32")]
 forward_impl!(AtomicI32 => i32);
-#[cfg(std_atomic64)]
+
+#[cfg(target_has_atomic = "64")]
 forward_impl!(AtomicI64 => i64);
+
+#[cfg(target_has_atomic = "ptr")]
 forward_impl!(AtomicIsize => isize);
 
+#[cfg(target_has_atomic = "8")]
 forward_impl!(AtomicU8 => u8);
+
+#[cfg(target_has_atomic = "16")]
 forward_impl!(AtomicU16 => u16);
+
+#[cfg(target_has_atomic = "32")]
 forward_impl!(AtomicU32 => u32);
-#[cfg(std_atomic64)]
+
+#[cfg(target_has_atomic = "64")]
 forward_impl!(AtomicU64 => u64);
+
+#[cfg(target_has_atomic = "ptr")]
 forward_impl!(AtomicUsize => usize);
 
 #[cfg(test)]