arm: Fix tst-gnu2-tls2

arm: Fix tst-gnu2-tls2

On armv7a vfpv4 tst-gnu2-tls2 fails with:

  open tst-gnu2-tls2mod0.so
  open tst-gnu2-tls2mod1.so
  open tst-gnu2-tls2mod2.so
  close tst-gnu2-tls2mod0.so
  close tst-gnu2-tls2mod1.so
  open tst-gnu2-tls2mod0.so
  open tst-gnu2-tls2mod1.so
  Didn't expect signal from child: got `Aborted'

Because AFTER_TLSDESC_CALL might clobber caller-saved registers and
the zero array might call the memset function resolution, which itself
might clobber some vector registers.

The AFTER_TLSDESC_CALL calls memset and memcmp, and both the
lazy resolution and the routines themselves can clobber the
caller-saved registes used in the tests.

Checked on arm-linux-gnueabihf (armv7-a vpfv4 / QEMU).

Reviewed-by: Florian Weimer <fweimer@redhat.com>