Add crt1-2.0.o for glibc 2.0 compatibility tests

Starting from glibc 2.1, crt1.o contains _IO_stdin_used which is checked
by _IO_check_libio to provide binary compatibility for glibc 2.0.  Add
crt1-2.0.o for tests against glibc 2.0.  Define tests-2.0 for glibc 2.0
compatibility tests.  Add and update glibc 2.0 compatibility tests for
stderr, matherr and pthread_kill.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>