sdext: use --switch=2 --readonly-tables gperf options

See 73ecb924 (Use --switch=2
--readonly-tables gperf options, 2014-04-13) for reasoning.

Change-Id: Ie1cfe753979d908077134b86587d8de5fa7c2ee8

sdext/CustomTarget_pdfimport.mk

@@ -16,6 +16,6 @@ $(call gb_CustomTarget_get_workdir,sdext/pdfimport)/hash.cxx : \
 		$(SRCDIR)/sdext/source/pdfimport/wrapper/keyword_list \
 		| $(call gb_CustomTarget_get_workdir,sdext/pdfimport)/.dir
 	$(call gb_Output_announce,$(subst $(WORKDIR)/,,$@),$(true),GPF,1)
-	$(GPERF) -C -t -l -L C++ -m 20 -Z PdfKeywordHash -k'4-5,$$' $< > $@
+	$(GPERF) -C -t -l -L C++ -m 20 --switch=2 --readonly-tables -Z PdfKeywordHash -k'4-5,$$' $< > $@
 
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