rustc: Provide compiler-rt sources

This is needed to build libprofiler_builtins now.

rust-lang/rust@e59f0cc#diff-daf9539767b10f18e1517f65cdc2e0e2
rust-lang/compiler-builtins#295

pkgs/development/compilers/rust/rustc.nix

@@ -1,6 +1,6 @@
 { stdenv, removeReferencesTo, pkgsBuildBuild, pkgsBuildHost, pkgsBuildTarget
 , fetchurl, file, python2, tzdata, ps
-, llvm_7, darwin, git, cmake, rustPlatform
+, llvmPackages_7, darwin, git, cmake, rustPlatform
 , which, libffi, gdb
 , withBundledLLVM ? false
 }:
@@ -9,13 +9,17 @@ let
   inherit (stdenv.lib) optional optionalString;
   inherit (darwin.apple_sdk.frameworks) Security;
 
-  llvmSharedForBuild = pkgsBuildBuild.llvm_7.override { enableSharedLibraries = true; };
-  llvmSharedForHost = pkgsBuildHost.llvm_7.override { enableSharedLibraries = true; };
-  llvmSharedForTarget = pkgsBuildTarget.llvm_7.override { enableSharedLibraries = true; };
+  llvmPackages = llvmPackages_7;
+
+  llvmSharedForBuild = pkgsBuildBuild.llvmPackages.llvm.override { enableSharedLibraries = true; };
+  llvmSharedForHost = pkgsBuildHost.llvmPackages.llvm.override { enableSharedLibraries = true; };
+  llvmSharedForTarget = pkgsBuildTarget.llvmPackages.llvm.override { enableSharedLibraries = true; };
 
   # For use at runtime
-  llvmShared = llvm_7.override { enableSharedLibraries = true; };
-in stdenv.mkDerivation rec {
+  llvmShared = llvmPackages.llvm.override { enableSharedLibraries = true; };
+in
+
+stdenv.mkDerivation rec {
   pname = "rustc";
   version = "1.37.0";
 
@@ -24,6 +28,12 @@ in stdenv.mkDerivation rec {
     sha256 = "1hrqprybhkhs6d9b5pjskfnc5z9v2l2gync7nb39qjb5s0h703hj";
   };
 
+  # Provide the compiler-rt sources needed for profiling.
+  preConfigure = ''
+    mkdir src/llvm-project/compiler-rt
+    tar xf ${llvmPackages.compiler-rt.src} -C src/llvm-project/compiler-rt --strip-components=1
+  '';
+
   __darwinAllowLocalNetworking = true;
 
   # rustc complains about modified source files otherwise