Add build script to set target configuration variable

Cargo.toml

@@ -2,6 +2,7 @@
 name = "libretunes"
 version = "0.1.0"
 edition = "2021"
+build = "src/build.rs"
 
 [lib]
 crate-type = ["cdylib", "rlib"]

src/build.rs

@@ -0,0 +1,9 @@
+// Set the target config variable to the target triple of the current build
+// This is used so we can determine the target triple at compile time
+// See https://stackoverflow.com/a/51311222
+fn main() {
+    println!(
+        "cargo:rustc-cfg=target=\"{}\"",
+        std::env::var("TARGET").unwrap()
+    );
+}