Merge remote-tracking branch 'remotes/rth/tags/pull-fpu-20181005' into staging

Testing infrastructure for softfpu (not run by default).
Drop countLeadingZeros.
Fix div_floats.
Add udiv_qrnnd specializations for x86_64, s390x, ppc64 hosts.

# gpg: Signature made Fri 05 Oct 2018 19:00:09 BST
# gpg:                using RSA key 64DF38E8AF7E215F
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>"
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A  05C0 64DF 38E8 AF7E 215F

* remotes/rth/tags/pull-fpu-20181005:
  softfloat: Specialize udiv_qrnnd for ppc64
  softfloat: Specialize udiv_qrnnd for s390x
  softfloat: Specialize udiv_qrnnd for x86_64
  softfloat: Fix division
  softfloat: Replace countLeadingZeros32/64 with clz32/64
  tests/fp/fp-test: add floating point tests
  gitmodules: add berkeley's softfloat + testfloat version 3
  softfloat: remove float64_trunc_to_int

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>