riscv64: fix DB_THREAD_SELF, fixes 4 testsuite failures
riscv64: fix DB_THREAD_SELF, fixes 4 testsuite failures

wbx-github/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,kraj/uclibc-ng,kraj/uclibc-ng