Rollup merge of rust-lang#63558 - jgalenson:move-remap, r=alexcrichton

Remap paths for proc-macro crates.

The remap-debuginfo config option remaps paths in most crates, but it does not apply to proc-macros, so they are still non-reproducible.  This patch fixes that.

I'm not completely sure if this is the best way to do this, but to get reproducible builds we need librustc_macros to be built with --remap-path-prefix.  I was previously modifying Cargo to pass that argument to all child crates, so this seems simpler and more correct.

I did not add a test since there do not seem to be any existing tests for RUSTC_DEBUGINFO_MAP.

r? @alexcrichton

src/bootstrap/bin/rustc.rs

@@ -276,10 +276,6 @@ fn main() {
                 cmd.arg("-C").arg("target-feature=-crt-static");
             }
         }
-
-        if let Ok(map) = env::var("RUSTC_DEBUGINFO_MAP") {
-            cmd.arg("--remap-path-prefix").arg(&map);
-        }
     } else {
         // Override linker if necessary.
         if let Ok(host_linker) = env::var("RUSTC_HOST_LINKER") {
@@ -296,6 +292,10 @@ fn main() {
         }
     }
 
+    if let Ok(map) = env::var("RUSTC_DEBUGINFO_MAP") {
+        cmd.arg("--remap-path-prefix").arg(&map);
+    }
+
     // Force all crates compiled by this compiler to (a) be unstable and (b)
     // allow the `rustc_private` feature to link to other unstable crates
     // also in the sysroot. We also do this for host crates, since those