message: performance miniapps: don't enable -march=native on ARM
  See e.g.
diff: @@ -98,7 +98,10 @@ MFEM_PERF_CXXFLAGS_gcc_ppc64 = -mcpu=native -mtune=native\
  MFEM_PERF_CXXFLAGS_xlc = -mcpu=native
  # - Clang extra options:
  +ifneq ($(MFEM_MACHINE),arm64)
  + # -march=native is unavailable for ARM
  MFEM_PERF_CXXFLAGS_clang += -march=native
  +endif
  MFEM_PERF_CXXFLAGS_clang += $(PEDANTIC_FLAG) -Wall
  MFEM_PERF_CXXFLAGS_clang += -fcolor-diagnostics
  MFEM_PERF_CXXFLAGS_clang += -fvectorize
  