glibc: add gettext to nativeBuildInputs

The `gettext` package is required in order to build and install the libc
message catalogs.

Previously, glibc was falling back to the C locale, even though the
default locale has been changed (e.g. to de_DE.UTF-8):
```
rm: das Entfernen von 'file' ist nicht möglich: No such file or directory
```

With this change, the whole string will be translated to the desired
locale:
```
rm: das Entfernen von 'file' ist nicht möglich: Datei oder Verzeichnis nicht gefunden
```

Signed-off-by: David Wronek <david.wronek@mainlining.org>

pkgs/development/libraries/glibc/common.nix

@@ -33,6 +33,7 @@
   libpng ? null,
   libidn2,
   bison,
+  gettext,
   python3Minimal,
 }:
 
@@ -237,6 +238,7 @@ stdenv.mkDerivation (
     depsBuildBuild = [ buildPackages.stdenv.cc ];
     nativeBuildInputs = [
       bison
+      gettext
       python3Minimal
     ]
     ++ extraNativeBuildInputs;