Since enabling LTO in Tumbleweed, the dovecot23 package fails to build most of
the time with

[  133s] libtool: link: gcc -std=gnu99 -O2 -Wall -D_FORTIFY_SOURCE=2
-fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables
-fstack-clash-protection -Werror=return-type -flto=auto -g -I/usr/lib64 -fpic
-DPIC -fstack-protector-strong -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2
-mfunction-return=thunk -mindirect-branch=thunk -Wall -W -Wmissing-prototypes
-Wmissing-declarations -Wpointer-arith -Wchar-subscripts -Wformat=2
-Wbad-function-cast -fno-builtin-strftime -Wstrict-aliasing=2
-DOPENSSL_LOAD_CONF -flto=auto -o test-iostream-ssl test-iostream-ssl.o -pie 
./.libs/libssl_iostream_openssl.so ./.libs/libssl_iostream.a
../lib-test/.libs/libtest.a ../lib/.libs/liblib.a -lssl -lcrypto -ldl
-Wl,-rpath
-Wl,/home/abuild/rpmbuild/BUILD/dovecot-2.3.8/src/lib-ssl-iostream/.libs
-Wl,-rpath -Wl,/usr/lib64/dovecot/modules
[  136s]
/usr/lib64/gcc/x86_64-suse-linux/9/../../../../x86_64-suse-linux/bin/ld:
test-iostream-ssl: hidden symbol `t_str_new' in
/tmp/test-iostream-ssl.X2QBZZ.ltrans0.ltrans.o is referenced by DSO
[  136s]
/usr/lib64/gcc/x86_64-suse-linux/9/../../../../x86_64-suse-linux/bin/ld: final
link failed: bad value
[  136s] collect2: error: ld returned 1 exit status
[  136s] make[3]: *** [Makefile:637: test-iostream-ssl] Error 1

Without changing anything, the build completes, but this is a rare occurrence.
Disabling LTO solves the build problem.