stdenv: use gcc external bootstrap

pkgs/development/libraries/glibc/default.nix

@@ -4,7 +4,7 @@
 , withGd ? false
 , withLibcrypt? false
 , buildPackages
-, enableCopyLibGccHack ? true
+, enableCopyLibGccHack ? !stdenv.enableGccExternalBootstrapForStdenv or false
 }:
 
 let
@@ -15,10 +15,12 @@ let
   ];
 in
 
+lib.pipe
 (callPackage ./common.nix { inherit stdenv; } {
   inherit withLinuxHeaders withGd profilingLibraries withLibcrypt;
   pname = "glibc" + lib.optionalString withGd "-gd";
-}).overrideAttrs(previousAttrs: {
+}) [
+  (pkg: pkg.overrideAttrs(previousAttrs: {
 
     # Note:
     # Things you write here override, and do not add to,
@@ -65,6 +67,27 @@ in
         ])
       ]);
 
+    # glibc needs to `dlopen()` `libgcc_s.so` (see `preInstall` phase below for
+    # why) but does not link against it.  Furthermore, glibc doesn't use the
+    # ordinary `dlopen()` call to do this; instead it uses one which ignores
+    # most paths:
+    #
+    #   https://sourceware.org/legacy-ml/libc-help/2013-11/msg00026.html
+    #
+    # In order to get it to not ignore `libgcc_s.so`, we have to add its path to
+    # `user-defined-trusted-dirs`:
+    #
+    #   https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/Makefile;h=b509b3eada1fb77bf81e2a0ca5740b94ad185764#l1355
+    #
+    # Conveniently, this will also inform Nix of the fact that glibc depends on
+    # gcc.libgcc, since the path will be embedded in the resulting binary.
+    #
+    makeFlags =
+      (previousAttrs.makeFlags or [])
+      ++ lib.optionals (!enableCopyLibGccHack && stdenv.cc.cc?libgcc) [
+        "user-defined-trusted-dirs=${stdenv.cc.cc.libgcc}/lib"
+      ];
+
     # Since glibc commit 9d79e0377b08773ec4f7ec38479b1563606f7ef7, Any program
     # which calls `pthread_cancel()` or `pthread_exit()` must be able to
     # `dlopen("libgcc_s.so")`.  If it cannot, `glibc` will abort the process.
@@ -170,6 +193,15 @@ in
 
     separateDebugInfo = true;
 
-  meta = (previousAttrs.meta or {}) // { description = "The GNU C Library"; };
-})
+    meta = (previousAttrs.meta or {}) // { description = "The GNU C Library"; };
+  }))
+
+  (pkg: pkg.overrideAttrs (previousAttrs: {
+    passthru = (previousAttrs.passthru or {}) // {
+      isFromBootstrapTools = false;
+    } // lib.optionalAttrs (!enableCopyLibGccHack && stdenv.cc.cc?libgcc) {
+      inherit (stdenv.cc.cc) libgcc;
+    };
+  }))
+]
 

pkgs/development/libraries/gmp/6.x.nix

@@ -27,6 +27,7 @@ let self = stdenv.mkDerivation rec {
   # - see #5855 for related discussion
   outputs = [ "out" "dev" "info" ];
   passthru.static = self.out;
+  passthru.isFromBootstrapFiles = false;
 
   strictDeps = true;
   depsBuildBuild = [ buildPackages.stdenv.cc ];

pkgs/development/libraries/isl/generic.nix

@@ -31,4 +31,5 @@ stdenv.mkDerivation {
     description = "A library for manipulating sets and relations of integer points bounded by linear constraints";
     platforms = lib.platforms.all;
   };
+  passthru.isFromBootstrapFiles = false;
 }

pkgs/development/libraries/libmpc/default.nix

@@ -38,4 +38,5 @@ stdenv.mkDerivation rec {
     platforms = lib.platforms.all;
     maintainers = [ ];
   };
+  passthru.isFromBootstrapFiles = false;
 }

pkgs/development/libraries/mpfr/default.nix

@@ -48,6 +48,7 @@ stdenv.mkDerivation rec {
           pcregrep -o1 '<title>GNU MPFR version ([0-9.]+)</title>')"
       update-source-version ${pname} "$new_version"
     '';
+    isFromBootstrapFiles = false;
   };
 
   meta = {