rustc: use the wrapper for fastCross sysroot

This avoids having two layers of wrapper for cross rustc.

pkgs/build-support/rust/rustc-wrapper/default.nix

@@ -1,4 +1,4 @@
-{ lib, runCommand, rustc-unwrapped }:
+{ lib, runCommand, rustc-unwrapped, sysroot ? null }:
 
 runCommand "${rustc-unwrapped.pname}-wrapper-${rustc-unwrapped.version}" {
   preferLocalBuild = true;
@@ -7,6 +7,7 @@ runCommand "${rustc-unwrapped.pname}-wrapper-${rustc-unwrapped.version}" {
 
   env = {
     prog = "${rustc-unwrapped}/bin/rustc";
+    sysroot = lib.optionalString (sysroot != null) "--sysroot ${sysroot}";
   };
 
   passthru = {

pkgs/build-support/rust/rustc-wrapper/rustc-wrapper.sh

@@ -1,11 +1,16 @@
 #!@shell@
 
+extraBefore=(@sysroot@)
+extraAfter=($NIX_RUSTFLAGS)
+
 # Optionally print debug info.
 if (( "${NIX_DEBUG:-0}" >= 1 )); then
+    echo "extra flags before to @prog@:" >&2
+    printf "  %q\n" "${extraBefore[@]}" >&2
     echo "original flags to @prog@:" >&2
     printf "  %q\n" "$@" >&2
     echo "extra flags after to @prog@:" >&2
-    printf "  %q\n" $NIX_RUSTFLAGS >&2
+    printf "  %q\n" "${extraAfter[@]}" >&2
 fi
 
-exec @prog@ "$@" $NIX_RUSTFLAGS
+exec @prog@ "${extraBefore[@]}" "$@" "${extraAfter[@]}"

pkgs/development/compilers/rust/1_74.nix

@@ -16,7 +16,7 @@
 , CoreFoundation, Security, SystemConfiguration
 , pkgsBuildTarget, pkgsBuildBuild, pkgsBuildHost
 , makeRustPlatform
-, wrapRustc
+, wrapRustcWith
 , llvmPackages_16, llvm_16
 } @ args:
 

pkgs/development/compilers/rust/default.nix

@@ -18,7 +18,7 @@
 , CoreFoundation, Security, SystemConfiguration
 , pkgsBuildBuild
 , makeRustPlatform
-, wrapRustc
+, wrapRustcWith
 }:
 
 let
@@ -76,7 +76,10 @@ in
         # Use boot package set to break cycle
         inherit (bootstrapRustPackages) cargo rustc rustfmt;
       });
-      rustc = wrapRustc self.rustc-unwrapped;
+      rustc = wrapRustcWith {
+        inherit (self) rustc-unwrapped;
+        sysroot = if fastCross then self.rustc-unwrapped else null;
+      };
       rustfmt = self.callPackage ./rustfmt.nix {
         inherit Security;
         inherit (self.buildRustPackages) rustc;

pkgs/development/compilers/rust/rustc.nix

@@ -169,7 +169,7 @@ in stdenv.mkDerivation (finalAttrs: {
 
     python ./x.py --keep-stage=0 --stage=1 install library/std
     mkdir -v $out/bin $doc $man
-    makeWrapper ${rustc.unwrapped}/bin/rustc $out/bin/rustc --add-flags "--sysroot $out"
+    ln -s ${rustc.unwrapped}/bin/rustc $out/bin
     makeWrapper ${rustc.unwrapped}/bin/rustdoc $out/bin/rustdoc --add-flags "--sysroot $out"
     ln -s ${rustc.unwrapped}/lib/rustlib/{manifest-rust-std-,}${stdenv.hostPlatform.rust.rustcTargetSpec} $out/lib/rustlib/
     echo rust-std-${stdenv.hostPlatform.rust.rustcTargetSpec} >> $out/lib/rustlib/components