Fixed compiler warnings regarding enum comparison.

Warnings like

  comparison of unsigned expression < 0 is always false

are reported with -Wextra when enum types that are compiled to an
unsigned type (which is up to the compiler) are checked for negativity.

src/libsimaka/simaka_message.c

@@ -139,7 +139,7 @@ ENUM(simaka_client_error_names, SIM_UNABLE_TO_PROCESS, SIM_RANDS_NOT_FRESH,
  */
 bool simaka_attribute_skippable(simaka_attribute_t attribute)
 {
-	bool skippable = !(attribute >= 0 && attribute <= 127);
+	bool skippable = !((int)attribute >= 0 && attribute <= 127);
 
 	DBG1(DBG_LIB, "%sskippable EAP-SIM/AKA attribute %N",
 		 skippable ? "ignoring " : "found non-",

src/libstrongswan/credentials/cred_encoding.c

@@ -116,7 +116,7 @@ METHOD(cred_encoding_t, get_cache, bool,
 {
 	chunk_t *chunk;
 
-	if (type >= CRED_ENCODING_MAX || type < 0)
+	if (type >= CRED_ENCODING_MAX || (int)type < 0)
 	{
 		return FALSE;
 	}
@@ -142,7 +142,7 @@ static bool encode(private_cred_encoding_t *this, cred_encoding_type_t type,
 	bool success = FALSE;
 	chunk_t *chunk;
 
-	if (type >= CRED_ENCODING_MAX || type < 0)
+	if (type >= CRED_ENCODING_MAX || (int)type < 0)
 	{
 		return FALSE;
 	}
@@ -195,7 +195,7 @@ METHOD(cred_encoding_t, cache, void,
 {
 	chunk_t *chunk;
 
-	if (type >= CRED_ENCODING_MAX || type < 0)
+	if (type >= CRED_ENCODING_MAX || (int)type < 0)
 	{
 		return free(encoding.ptr);
 	}

src/libstrongswan/processing/processor.c

@@ -230,7 +230,7 @@ METHOD(processor_t, get_idle_threads, u_int,
  */
 static job_priority_t sane_prio(job_priority_t prio)
 {
-	if (prio < 0 || prio >= JOB_PRIO_MAX)
+	if ((int)prio < 0 || prio >= JOB_PRIO_MAX)
 	{
 		return JOB_PRIO_MAX - 1;
 	}

src/starter/confread.c

@@ -137,7 +137,7 @@ static void load_setup(starter_config_t *cfg, config_parsed_t *cfgp)
 
 		kw_token_t token = kw->entry->token;
 
-		if (token < KW_SETUP_FIRST || token > KW_SETUP_LAST)
+		if ((int)token < KW_SETUP_FIRST || token > KW_SETUP_LAST)
 		{
 			plog("# unsupported keyword '%s' in config setup", kw->entry->name);
 			cfg->err++;