Import 'ryu' crate version 1.0.5

Bug: 163175424
Test: N/A
Change-Id: I7bda5411adccb26198c53ed1cb41fc6bb08468d7
diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..f48477a
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,40 @@
+use std::env;
+use std::process::Command;
+use std::str::{self, FromStr};
+
+// The rustc-cfg strings below are *not* public API. Please let us know by
+// opening a GitHub issue if your build environment requires some way to enable
+// these cfgs other than by executing our build script.
+fn main() {
+    let minor = match rustc_minor_version() {
+        Some(minor) => minor,
+        None => return,
+    };
+
+    let target = env::var("TARGET").unwrap();
+    let emscripten = target == "asmjs-unknown-emscripten" || target == "wasm32-unknown-emscripten";
+
+    // 128-bit integers disabled on Emscripten targets as Emscripten doesn't
+    // currently support integers larger than 64 bits.
+    if !emscripten {
+        println!("cargo:rustc-cfg=integer128");
+    }
+
+    // MaybeUninit<T> stabilized in Rust 1.36:
+    // https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html
+    if minor >= 36 {
+        println!("cargo:rustc-cfg=maybe_uninit");
+    }
+}
+
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = env::var_os("RUSTC")?;
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    let next = pieces.next()?;
+    u32::from_str(next).ok()
+}