Don't rely on __noChroot for corepkgs

This doesn't work anymore if the "strict" chroot mode is
enabled. Instead, add Nix's store path as a dependency. This ensures
that its closure is present in the chroot.

corepkgs/buildenv.nix

@@ -23,6 +23,5 @@ derivation {
   # network traffic, so don't do that.
   preferLocalBuild = true;
 
-  # Don't build in a chroot because Nix's dependencies may not be there.
-  __noChroot = true;
+  inherit chrootDeps;
 }

corepkgs/config.nix.in

@@ -2,7 +2,7 @@ let
   fromEnv = var: def:
     let val = builtins.getEnv var; in
     if val != "" then val else def;
-in {
+in rec {
   perl = "@perl@";
   shell = "@bash@";
   coreutils = "@coreutils@";
@@ -14,4 +14,14 @@ in {
   tr = "@tr@";
   curl = "@curl@";
   nixBinDir = fromEnv "NIX_BIN_DIR" "@bindir@";
+  nixPrefix = "@prefix@";
+
+  # If Nix is installed in the Nix store, then automatically add it as
+  # a dependency to the core packages. This ensures that they work
+  # properly in a chroot.
+  chrootDeps =
+    if dirOf nixPrefix == builtins.storeDir then
+      [ (builtins.storePath nixPrefix) ]
+    else
+      [ ];
 }

corepkgs/fetchurl.nix

@@ -32,9 +32,6 @@ derivation {
   # No need to double the amount of network traffic
   preferLocalBuild = true;
 
-  # Don't build in a chroot because Nix's dependencies may not be there.
-  __noChroot = true;
-
   impureEnvVars = [
     # We borrow these environment variables from the caller to allow
     # easy proxy configuration.  This is impure, but a fixed-output
@@ -42,4 +39,6 @@ derivation {
     # by definition pure.
     "http_proxy" "https_proxy" "ftp_proxy" "all_proxy" "no_proxy"
   ];
+
+  inherit chrootDeps;
 }

corepkgs/nar.nix

@@ -41,9 +41,8 @@ derivation {
   args = [ "-e" builder ];
   inherit storePath hashAlgo compressionType;
 
-  # Don't build in a chroot because Nix's dependencies may not be there.
-  __noChroot = true;
-
   # Remote machines may not have ${nixBinDir} or ${coreutils} in the same prefixes
   preferLocalBuild = true;
+
+  inherit chrootDeps;
 }

corepkgs/unpack-channel.nix

@@ -37,6 +37,5 @@ derivation {
   # No point in doing this remotely.
   preferLocalBuild = true;
 
-  # Don't build in a chroot because Nix's dependencies may not be there.
-  __noChroot = true;
+  inherit chrootDeps;
 }

src/libexpr/primops.cc

@@ -1507,12 +1507,15 @@ void EvalState::createBaseEnv()
     mkInt(v, time(0));
     addConstant("__currentTime", v);
 
-    mkString(v, settings.thisSystem.c_str());
+    mkString(v, settings.thisSystem);
     addConstant("__currentSystem", v);
 
-    mkString(v, nixVersion.c_str());
+    mkString(v, nixVersion);
     addConstant("__nixVersion", v);
 
+    mkString(v, settings.nixStore);
+    addConstant("__storeDir", v);
+
     /* Language version.  This should be increased every time a new
        language feature gets added.  It's not necessary to increase it
        when primops get added, because you can just use `builtins ?