cmake: correctly detect clang compiler on macOS

pkgs/development/tools/build-managers/cmake/setup-hook.sh

@@ -55,6 +55,9 @@ cmakeConfigurePhase() {
     # we don't want our binaries to have a "minimum" OSX version
     cmakeFlags="-DCMAKE_OSX_DEPLOYMENT_TARGET= $cmakeFlags"
 
+    # correctly detect our clang compiler
+    cmakeFlags="-DCMAKE_POLICY_DEFAULT_CMP0025=NEW $cmakeFlags"
+
     # This installs shared libraries with a fully-specified install
     # name. By default, cmake installs shared libraries with just the
     # basename as the install name, which means that, on Darwin, they