glibc: split getent into its own output

Many dependents only require getent and not all the locale generation
tools that are included in the `bin` output. This can save some
closure size!

nixos/doc/manual/release-notes/rl-2311.section.md

···
 
 - `mariadb` now defaults to `mariadb_1011` instead of `mariadb_106`, meaning the default version was upgraded from 10.6.x to 10.11.x. See the [upgrade notes](https://mariadb.com/kb/en/upgrading-from-mariadb-10-6-to-mariadb-10-11/) for potential issues.
 
+- `getent` has been moved from `glibc`'s `bin` output to its own dedicated output, reducing closure size for many dependents. Dependents using the `getent` alias should not be affected; others should move from using `glibc.bin` or `getBin glibc` to `getent` (which also improves compatibility with non-glibc platforms).
+
 - `etcd` has been updated to 3.5, you will want to read the [3.3 to 3.4](https://etcd.io/docs/v3.5/upgrades/upgrade_3_4/) and [3.4 to 3.5](https://etcd.io/docs/v3.5/upgrades/upgrade_3_5/) upgrade guides
 
 - `himalaya` has been updated to `0.8.0`, which drops the native TLS support (in favor of Rustls) and add OAuth 2.0 support. See the [release note](https://github.com/soywod/himalaya/releases/tag/v0.8.0) for more details.

pkgs/development/libraries/glibc/common.nix

···
     "OBJCOPY=${stdenv.cc.targetPrefix}objcopy"
   ];
 
+  postInstall = (args.postInstall or "") + ''
+    moveToOutput bin/getent $getent
+  '';
+
   installFlags = [ "sysconfdir=$(out)/etc" ];
 
   # out as the first output is an exception exclusive to glibc
-  outputs = [ "out" "bin" "dev" "static" ];
+
+  # getent is its own output, not kept in bin, since many things
+  # depend on getent but not on the locale generation tools in the bin
+  # output. This saves a couple of megabytes of closure size in many cases.
+  outputs = [ "out" "bin" "dev" "static" "getent" ];
 
   strictDeps = true;
   depsBuildBuild = [ buildPackages.stdenv.cc ];
···
   passthru = { inherit version; minorRelease = version; };
 }
 
-// (removeAttrs args [ "withLinuxHeaders" "withGd" ]) //
+// (removeAttrs args [ "withLinuxHeaders" "withGd" "postInstall" ]) //
 
 {
   src = fetchurl {

pkgs/development/libraries/glibc/default.nix

···
         "user-defined-trusted-dirs=${stdenv.cc.cc.libgcc}/lib"
       ];
 
-    postInstall = (if stdenv.hostPlatform == stdenv.buildPlatform then ''
+    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 ''

pkgs/top-level/unixtools.nix

···
       darwin = pkgs.darwin.system_cmds;
     };
     getent = {
-      linux = if stdenv.hostPlatform.libc == "glibc" then pkgs.stdenv.cc.libc
+      linux = if stdenv.hostPlatform.libc == "glibc" then pkgs.stdenv.cc.libc.getent
               else pkgs.netbsd.getent;
       darwin = pkgs.netbsd.getent;
     };