-fsanitize=undefined is not the same thing as --enable-sanitizers. After
commit 47c823e ("tests/docker: add sanitizers back to clang build", 2019-09-11)
test-clang is almost duplicating the asan (test-debug) test, so
partly revert commit 47c823e5b while leaving ubsan enabled.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
9e5ef16491