build-sys: add check for gperf lookup function signature (#5055)

gperf-3.1 generates lookup functions that take a size_t length
parameter instead of unsigned int. Test for this at configure time.

Fixes: https://github.com/systemd/systemd/issues/5039

src/network/netdev/netdev.h

@@ -175,7 +175,7 @@ NetDevKind netdev_kind_from_string(const char *d) _pure_;
 int config_parse_netdev_kind(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 
 /* gperf */
-const struct ConfigPerfItem* network_netdev_gperf_lookup(const char *key, unsigned length);
+const struct ConfigPerfItem* network_netdev_gperf_lookup(const char *key, GPERF_LEN_TYPE length);
 
 /* Macros which append INTERFACE= to the message */
 

src/network/networkd-conf.h

@@ -23,7 +23,7 @@ typedef struct Manager Manager;
 
 int manager_parse_config_file(Manager *m);
 
-const struct ConfigPerfItem* networkd_gperf_lookup(const char *key, unsigned length);
+const struct ConfigPerfItem* networkd_gperf_lookup(const char *key, GPERF_LEN_TYPE length);
 
 int config_parse_duid_type(
                 const char *unit,

src/network/networkd-network.h

@@ -244,7 +244,7 @@ int config_parse_ntp(const char *unit, const char *filename, unsigned line, cons
 /* Legacy IPv4LL support */
 int config_parse_ipv4ll(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 
-const struct ConfigPerfItem* network_network_gperf_lookup(const char *key, unsigned length);
+const struct ConfigPerfItem* network_network_gperf_lookup(const char *key, GPERF_LEN_TYPE length);
 
 extern const sd_bus_vtable network_vtable[];