Check for gperf, add support to the build system

configure.in

@@ -12,6 +12,12 @@ AC_PROG_CC
 AM_PROG_CC_C_O
 LT_INIT([disable-static])
 
+AC_CHECK_PROG(GPERF, [gperf], [gperf])
+if test "x$GPERF" = x; then
+	AC_MSG_ERROR([GNU gperf not found, please install it])
+fi
+AC_SUBST(GPERF)
+
 AC_CHECK_PROG(ANTLR, [antlr3], [antlr3])
 if test "x$ANTLR" = x; then
 	if test -d $srcdir/src/pregen; then

src/Makefile.am

@@ -21,6 +21,10 @@ if COND_OSS4
 OSS4SRC=laudio_oss4.c
 endif
 
+GPERF_FILES =
+
+GPERF_PRODUCTS =
+
 ANTLR_GRAMMARS = \
 	RSP.g RSP2SQL.g \
 	DAAP.g DAAP2SQL.g
@@ -82,15 +86,33 @@ forked_daapd_SOURCES = main.c \
 nodist_forked_daapd_SOURCES = \
 	$(ANTLR_SOURCES)
 
+BUILT_SOURCES = \
+	$(GPERF_PRODUCTS)
+
 EXTRA_DIST = \
 	$(ANTLR_GRAMMARS) \
 	scan-mpc.c \
 	scan-flac.c
 
+CLEANFILES = \
+	$(GPERF_PRODUCTS)
+
 # Let's help the dependencies a little.
 rsp_query.c: RSPLexer.h RSPParser.h RSP2SQL.h
 daap_query.c: DAAPLexer.h DAAPParser.h DAAP2SQL.h
 
+# gperf construction rules
+%_hash.c: %.gperf
+	if $(GPERF) $< > $@.tmp; then \
+		mv $@.tmp $@; \
+	elif $(GPERF) --version >/dev/null 2>&1; then \
+		rm $@.tmp; \
+		exit 1; \
+	else \
+		rm $@.tmp; \
+		touch $@; \
+	fi
+
 # Support for building the parsers when ANTLR3 is available
 if COND_ANTLR
 SUFFIXES = .g .u