cling: use cmakeBuildType instead of explicit -D

Ref: https://github.com/NixOS/nixpkgs/issues/427019
Ref: https://nixos.org/manual/nixpkgs/stable/#cmake-build-type

pkgs/by-name/cl/cling/package.nix

@@ -79,6 +79,8 @@ let
 
     strictDeps = true;
 
+    cmakeBuildType = if debug then "Debug" else "Release";
+
     cmakeFlags = [
       "-DLLVM_EXTERNAL_PROJECTS=cling"
       "-DLLVM_EXTERNAL_CLING_SOURCE_DIR=../../cling-source"
@@ -87,12 +89,6 @@ let
       "-DLLVM_INCLUDE_TESTS=OFF"
       "-DLLVM_ENABLE_RTTI=ON"
     ]
-    ++ lib.optionals (!debug) [
-      "-DCMAKE_BUILD_TYPE=Release"
-    ]
-    ++ lib.optionals debug [
-      "-DCMAKE_BUILD_TYPE=Debug"
-    ]
     ++ lib.optionals useLLVMLibcxx [
       "-DLLVM_ENABLE_LIBCXX=ON"
       "-DLLVM_ENABLE_LIBCXXABI=ON"