--- a/library/std/build.rs
+++ b/library/std/build.rs
@@ -1,6 +1,39 @@
 use std::env;

 fn main() {
+    // MacPorts Legacy Support for macOS < 10.12
+    // Provides missing POSIX functions like clock_gettime, CLOCK_UPTIME_RAW, etc.
+    if env::var_os("MACPORTS_LEGACY_SUPPORT_ENABLED")
+        .map(|s| s.to_string_lossy() == "1")
+        .unwrap_or(false)
+    {
+        let str = env::var_os("MACPORTS_LEGACY_SUPPORT_LDFLAGS")
+            .map(|s| s.to_string_lossy().to_string())
+            .expect("MACPORTS_LEGACY_SUPPORT_LDFLAGS shouldn't be empty");
+        let (path, mut name) = str
+            .strip_suffix(".a")
+            .expect("MACPORTS_LEGACY_SUPPORT_LDFLAGS should be static library")
+            .split_at(str.rfind("/").unwrap_or(0));
+        name = name.strip_prefix("/lib").unwrap_or(name);
+        if path.len() > 0 {
+            println!("cargo:rustc-link-search=native={}", path);
+        }
+        if name.len() == 0 {
+            panic!("MACPORTS_LEGACY_SUPPORT_LDFLAGS should contain library name")
+        }
+        println!("cargo:rustc-link-lib=static={}", name);
+    }
+
+    // Emulated TLS support for macOS < 10.7
+    // Compiles LLVM's emutls.c to provide __thread variable support
+    if cfg!(target_os = "macos") && cfg!(target_enforce_emulated_tls) {
+        let mut emutls_cfg = cc::Build::new();
+        emutls_cfg.warnings(false);
+        emutls_cfg
+            .file("../../src/llvm-project/compiler-rt/lib/builtins/emutls.c")
+            .compile("emutls");
+    }
+
     println!("cargo:rerun-if-changed=build.rs");
     let target = env::var("TARGET").expect("TARGET was not set");