glibc: make crypt support optional

The libcrypt library is going to be replaced with libxcrypt in packages
that require it.

pkgs/development/libraries/glibc/common.nix

···
 , withLinuxHeaders ? false
 , profilingLibraries ? false
 , withGd ? false
+, withLibcrypt ? false
 , meta
 , extraBuildInputs ? []
 , extraNativeBuildInputs ? []
···
       # To avoid linking with -lgcc_s (dynamic link)
       # so the glibc does not depend on its compiler store path
       "libc_cv_as_needed=no"
-    ] ++ lib.optional withGd "--with-gd";
+    ]
+    ++ lib.optional withGd "--with-gd"
+    ++ lib.optional (!withLibcrypt) "--disable-crypt";
 
   makeFlags = [
     "OBJCOPY=${stdenv.cc.targetPrefix}objcopy"

pkgs/development/libraries/glibc/default.nix

···
 , withLinuxHeaders ? true
 , profilingLibraries ? false
 , withGd ? false
+, withLibcrypt? false
 , buildPackages
 }:
 
···
 callPackage ./common.nix { inherit stdenv; } {
     pname = "glibc" + lib.optionalString withGd "-gd";
 
-    inherit withLinuxHeaders profilingLibraries withGd;
+    inherit withLinuxHeaders profilingLibraries withGd withLibcrypt;
 
     # Note:
     # Things you write here override, and do not add to,