Add CONFIG_FEATURE_SYSLOG which controls whether
bb_xx_msg will ever try to send output to syslog.
Add "select CONFIG_FEATURE_SYSLOG" to relevant applets.
This allows to omit syslog code if we do not have
any syslog-capable applets in the build.

diff --git a/libbb/verror_msg.c b/libbb/verror_msg.c
index 237547d..be206e4 100644
--- a/libbb/verror_msg.c
+++ b/libbb/verror_msg.c
@@ -32,7 +32,7 @@
 		else
 			fprintf(stderr, ": %s\n", strerr);
 	}
-	if (logmode & LOGMODE_SYSLOG) {
+	if (ENABLE_FEATURE_SYSLOG & (logmode & LOGMODE_SYSLOG)) {
 		if (!strerr)
 			vsyslog(LOG_ERR, s, p2);
 		else  {