message: makefile: add missing parenthesis to conditional
  This commit adds a missing parenthesis to a conditional in the MFEM
  makefile that checks if PREFIX is set when MFEM_USE_OCCA equals YES.
diff: @@ -346,7 +346,7 @@ ifneq (,$(filter install,$(MAKECMDGOALS)))
  @MFEM_EXT_LIBS@
  MFEM_LIB_FILE = @MFEM_LIB_DIR@/libmfem.$(if $(shared),$(SO_VER),a)
  ifeq ($(MFEM_USE_OCCA),YES)
  - ifneq ($(MFEM_INSTALL_DIR),$(abspath $(PREFIX))
  + ifneq ($(MFEM_INSTALL_DIR),$(abspath $(PREFIX)))
  $(error OCCA is enabled: PREFIX must be set during configuration!)
  endif
  endif
  