message: Add makefile-style deprecation warning
diff: @@ -351,7 +351,7 @@ doc:
  -include $(BLD)deps.mk
  -$(BLD)libmfem.a: $(OBJECT_FILES)
  +$(BLD)libmfem.a: deprecation-warnings $(OBJECT_FILES)
  $(AR) $(ARFLAGS) $(@) $(OBJECT_FILES)
  $(RANLIB) $(@)
  @@ -543,6 +543,11 @@ FORMAT_FILES = $(foreach dir,$(DIRS) $(EM_DIRS) config,"$(dir)/*.?pp")
  FORMAT_FILES += "tests/unit/*.cpp"
  FORMAT_FILES += $(foreach dir,$(DIRS),"tests/unit/$(dir)/*.?pp")
  +DEPRECATION_WARNING := "This feature is planned for removal in the next release. Please open an issue at github.com/mfem/mfem/issues if you depend on it."
  +.PHONY: deprecation-warnings
  +deprecation-warnings:
  + @if [ $(MFEM_USE_OPENMP) = YES ]; then echo [MFEM_USE_OPENMP]: $(DEPRECATION_WARNING); fi
  +
  style:
  @if ! $(ASTYLE) $(FORMAT_FILES) | grep Formatted; then\
  echo "No source files were changed.";\
  