I have add -lpthread to LDFLAGS
/bin/sh ../libtool --tag=CC --mode=link arm-linux-gcc -g -O2 -pthread -Wall -Wextra -Wpedantic -Wformat=2 -Wconversion -Wno-long-long -Wno-deprecated-declarations -fPIE -D_FORTIFY_SOURCE=2 -L/mnt/dists/openssl-v1.1.1i//lib64 -L/mnt/dists/openssl-v1.1.1i//lib -lssl -lcrypto -lpthread -fPIE -pie -Wl,-z,relro -Wl,-z,now -Wl,-z,noexecstack -o stunnel stunnel-tls.o stunnel-str.o stunnel-file.o stunnel-client.o stunnel-log.o stunnel-options.o stunnel-protocol.o stunnel-network.o stunnel-resolver.o stunnel-ssl.o stunnel-ctx.o stunnel-verify.o stunnel-sthreads.o stunnel-fd.o stunnel-dhparam.o stunnel-cron.o stunnel-stunnel.o stunnel-pty.o stunnel-libwrap.o stunnel-ui_unix.o
but still running error
EchoLife_WAP /tmp # ./stunnel
/tmp/stunnel: symbol '__ctype_b_loc': can't resolve symbol
/tmp/stunnel: symbol 'pthread_key_create': can't resolve symbol
/tmp/stunnel: symbol 'pthread_attr_setstacksize': can't resolve symbol
/tmp/stunnel: symbol 'pthread_sigmask': can't resolve symbol
/tmp/stunnel: symbol 'pthread_getspecific': can't resolve symbol
/tmp/stunnel: symbol 'pthread_create': can't resolve symbol
/tmp/stunnel: symbol 'openpty': can't resolve symbol
/tmp/stunnel: symbol 'pthread_detach': can't resolve symbol
/tmp/stunnel: symbol 'pthread_setspecific': can't resolve symbol
/tmp/stunnel: symbol 'pthread_join': can't resolve symbol