elf/tst-libc_dlvsym: Add a TEST_COMPAT around some symbol tests

The _sys_errlist and _sys_siglist symbols are deprecated since 2.32.
This patch adds a TEST_COMPAT check around the tests. This fixes test
failures on new architectures (such as RV32) that don't have this
symbol defined.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>