From cefd832d8957ad369bfb3923e4ebfd7a4c985973 Mon Sep 17 00:00:00 2001
From: Joel Galenson <jgalenson@google.com>
Date: Mon, 19 Aug 2019 09:30:45 -0700
Subject: [PATCH] Support deterministic builds by remapping the __FILE__ prefix
 if the compiler supports it.

---
 library/compiler-builtins/build.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/library/compiler-builtins/build.rs b/library/compiler-builtins/build.rs
index c714bc15de30..feb7fc6ecdab 100644
--- a/library/compiler-builtins/build.rs
+++ b/library/compiler-builtins/build.rs
@@ -423,6 +423,10 @@ mod c {
             panic!("RUST_COMPILER_RT_ROOT={} does not exist", root.display());
         }
 
+        // Support deterministic builds by remapping the __FILE__ prefix if the
+        // compiler supports it.
+        cfg.flag_if_supported(&format!("-ffile-prefix-map={}=.", root.display()));
+
         let src_dir = root.join("lib/builtins");
         for (sym, src) in sources.map.iter() {
             let src = src_dir.join(src);