It appears that the containerized test tst-setvbuf2 runs in a container without libgcc_s installed. Here's a log of a recently encountered failure in a CI run of the "upstream-testsuite" wrapper:

Running 'TIMEOUTFACTOR=20 /tmp/tmp.irjn8XGqQK/testsuite-wrapper make -i -j4 -k test-wrapper=/tmp/tmp.irjn8XGqQK/test-wrapper-sysso test t=stdio-common/tst-setvbuf2 2>&1 >> /root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/build.log'
../Rules:231: target '/root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/stdio-common/tst-setvbuf2' given more than once in the same rule
../Rules:231: target '/root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/stdio-common/tst-setvbuf2-ind' given more than once in the same rule
libgcc_s.so.1 must be installed for pthread_cancel to work
:: [ 10:12:10 ] :: [ LOG ] :: Output of 'TIMEOUTFACTOR=20 /tmp/tmp.irjn8XGqQK/testsuite-wrapper make -i -j4 -k test-wrapper=/tmp/tmp.irjn8XGqQK/test-wrapper-sysso test t=stdio-common/tst-setvbuf2 2>&1 >> /root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/build.log':
:: [ 10:12:10 ] :: [ LOG ] :: --------------- OUTPUT START ---------------
:: [ 10:12:10 ] :: [ LOG ] :: ../Rules:231: target '/root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/stdio-common/tst-setvbuf2' given more than once in the same rule
:: [ 10:12:10 ] :: [ LOG ] :: ../Rules:231: target '/root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/stdio-common/tst-setvbuf2-ind' given more than once in the same rule
:: [ 10:12:10 ] :: [ LOG ] :: libgcc_s.so.1 must be installed for pthread_cancel to work
:: [ 10:12:10 ] :: [ LOG ] :: --------------- OUTPUT END ---------------
:: [ 10:12:10 ] :: [ PASS ] :: Command 'TIMEOUTFACTOR=20 /tmp/tmp.irjn8XGqQK/testsuite-wrapper make -i -j4 -k test-wrapper=/tmp/tmp.irjn8XGqQK/test-wrapper-sysso test t=stdio-common/tst-setvbuf2 2>&1 >> /root/rpmbuild/BUILD/glibc-2.34/build-aarch64-redhat-linux/build.log' (Expected 0, got 0)
:: [ 10:12:10 ] :: [ FAIL ] :: File 'stdio-common/tst-setvbuf2.test-result' should contain 'PASS'