The gettid() function is available on Linux in glibc only since version
2.30. There are supported distributions that still use older glibc
version. Thus add a configure check if the gettid() function is
available and extend the check in src/prof_stack_range.c so it's skipped
also when gettid() isn't available.
Fixes: https://github.com/jemalloc/jemalloc/issues/2740