cctools: support LTO on Darwin

LTO is disabled during bootstrap to keep the bootstrap tools small and
avoid unnecessary LLVM rebuilds, but is enabled in the final stdenv
stage and should be usable by normal packages.

pkgs/stdenv/darwin/make-bootstrap-tools.nix

@@ -12,6 +12,10 @@ in rec {
     singleBinary = false;
   });
 
+  # We want a version of cctools without LLVM, because the LTO support ends up making
+  # the bootstrap tools huge and isn't really necessary for bootstrap
+  cctools_ = darwin.cctools.override { llvm = null; };
+
   # Avoid debugging larger changes for now.
   bzip2_ = bzip2.override (args: { linkStatic = true; });
 
@@ -95,7 +99,7 @@ in rec {
 
       # Copy binutils.
       for i in as ld ar ranlib nm strip otool install_name_tool dsymutil lipo; do
-        cp ${darwin.cctools}/bin/$i $out/bin
+        cp ${cctools_}/bin/$i $out/bin
       done
 
       cp -rd ${pkgs.darwin.CF}/Library $out
@@ -105,9 +109,9 @@ in rec {
       nuke-refs $out/bin/*
 
       rpathify() {
-        local libs=$(${darwin.cctools}/bin/otool -L "$1" | tail -n +2 | grep -o "$NIX_STORE.*-\S*") || true
+        local libs=$(${cctools_}/bin/otool -L "$1" | tail -n +2 | grep -o "$NIX_STORE.*-\S*") || true
         for lib in $libs; do
-          ${darwin.cctools}/bin/install_name_tool -change $lib "@rpath/$(basename $lib)" "$1"
+          ${cctools_}/bin/install_name_tool -change $lib "@rpath/$(basename $lib)" "$1"
         done
       }