fix: packages: dd4hep: %clang

Author: wdconinc

spack-environment/packages.yaml

@@ -103,7 +103,7 @@ packages:
     - '@1.16.2:'
   dd4hep:
     require:
-    - '%gcc'
+    - '%clang'  # ACTS requires same compiler as DD4hep since compiler options reused
     - '@1.32.1'
     - +ddg4 +ddcad +hepmc3 +xercesc
     - any_of: [+ddeve +utilityapps, -ddeve -utilityapps] # FIXME ^root +x +opengl when +utilityapps