message: Take a copy of spec.cxxflags in mfem package
  Workaround pending
diff: @@ -493,7 +493,7 @@ class Mfem(Package, CudaPackage, ROCmPackage):
  'MFEM_MPIEXEC=%s' % mfem_mpiexec,
  'MFEM_MPIEXEC_NP=%s' % mfem_mpiexec_np]
  - cxxflags = spec.compiler_flags['cxxflags']
  + cxxflags = spec.compiler_flags['cxxflags'][:]
  if cxxflags:
  # Add opt/debug flags if they are not present in global cxx flags
  