Fix gettid() after clone().

The tid is cached in the pthread_internal_t and is properly re-set after fork()
and pthread_create(). But after a plain clone() the value is stale from the
parent.

Test: mmma bionic/tests
Test: bionic-unit-tests-static --gtest_filter=*fork*:*clone*
Test: m checkbuild tests
Test: angler boots

Bug: 32305649
Change-Id: I026d416d1537484cd3e05c8493a35e5ed2acc8ed