glibc: use (lib.getBin pkgsBuildBuild.glibc) to generate locales

This is an alternative resolution of the problem identified in

  #259964

which stated that "glibc depends on buildPackages.glibc for locale
things.  buildPackages.glibc depended on buildPackages.libgcc,
which, since it's GCC, depends on the target's bintools, which
depend on the target's glibc, which, again, depends on
buildPackages.glibc, causing an infinute recursion when evaluating
buildPackages.glibc when glibc hasn't come from stdenv (e.g. on
musl)."

The fact that we use pkgsBuildHost.glibc instead of
pkgsBuildBuild.glibc to generate the locales has always been a gross
hack.  If we simply remove the gross hack the circularity goes away.

pkgs/development/libraries/glibc/default.nix

@@ -3,7 +3,7 @@
 , profilingLibraries ? false
 , withGd ? false
 , withLibcrypt? false
-, buildPackages
+, pkgsBuildBuild
 , libgcc
 }:
 
@@ -98,14 +98,23 @@ in
     postInstall = previousAttrs.postInstall + (if stdenv.hostPlatform == stdenv.buildPlatform then ''
       echo SUPPORTED-LOCALES=C.UTF-8/UTF-8 > ../glibc-2*/localedata/SUPPORTED
       make -j''${NIX_BUILD_CORES:-1} localedata/install-locales
-    '' else lib.optionalString stdenv.buildPlatform.isLinux ''
+    '' else lib.optionalString stdenv.buildPlatform.isLinux
       # This is based on http://www.linuxfromscratch.org/lfs/view/development/chapter06/glibc.html
       # Instead of using their patch to build a build-native localedef,
-      # we simply use the one from buildPackages
+      # we simply use the one from pkgsBuildBuild.
+      #
+      # Note that we can't use pkgsBuildHost (aka buildPackages) here, because
+      # that will cause an eval-time infinite recursion: "buildPackages.glibc
+      # depended on buildPackages.libgcc, which, since it's GCC, depends on the
+      # target's bintools, which depend on the target's glibc, which, again,
+      # depends on buildPackages.glibc, causing an infinute recursion when
+      # evaluating buildPackages.glibc when glibc hasn't come from stdenv
+      # (e.g. on musl)." https://github.com/NixOS/nixpkgs/pull/259964
+    ''
       pushd ../glibc-2*/localedata
       export I18NPATH=$PWD GCONV_PATH=$PWD/../iconvdata
-      mkdir -p $NIX_BUILD_TOP/${buildPackages.glibc}/lib/locale
-      ${lib.getBin buildPackages.glibc}/bin/localedef \
+      mkdir -p $NIX_BUILD_TOP/${pkgsBuildBuild.glibc}/lib/locale
+      ${lib.getBin pkgsBuildBuild.glibc}/bin/localedef \
         --alias-file=../intl/locale.alias \
         -i locales/C \
         -f charmaps/UTF-8 \
@@ -115,7 +124,7 @@ in
           else
             "--big-endian"} \
         C.UTF-8
-      cp -r $NIX_BUILD_TOP/${buildPackages.glibc}/lib/locale $out/lib
+      cp -r $NIX_BUILD_TOP/${pkgsBuildBuild.glibc}/lib/locale $out/lib
       popd
     '') + ''