llvmPackages*.lldb: fixup input by disabling libedit

Fixes #20773.  https://llvm.org/bugs/show_bug.cgi?id=28898
Of course, feel free to find a better solution.

I love this copy&paste :-/

pkgs/development/compilers/llvm/3.8/lldb.nix

@@ -36,6 +36,7 @@ stdenv.mkDerivation {
     "-DCLANG_MAIN_INCLUDE_DIR=${clang-unwrapped}/include"
     "-DPYTHON_VERSION_MAJOR=2"
     "-DPYTHON_VERSION_MINOR=7"
+    "-DLLDB_DISABLE_LIBEDIT=1" # https://llvm.org/bugs/show_bug.cgi?id=28898
   ];
 
   enableParallelBuilding = true;