Merge remote-tracking branch 'remotes/rth/tags/pull-mb-20201014' into staging

Implement rt signal frames for microblaze-linux-user
Adjust linux-user test for musl

# gpg: Signature made Thu 15 Oct 2020 05:50:00 BST
# gpg:                using RSA key 7A481E78868B4DB6A85A05C064DF38E8AF7E215F
# gpg:                issuer "richard.henderson@linaro.org"
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>" [full]
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A  05C0 64DF 38E8 AF7E 215F

* remotes/rth/tags/pull-mb-20201014:
  linux-user/microblaze: Remove non-rt signal frames
  linux-user/microblaze: Implement rt signal frames
  tests/tcg/linux-test: Adjust getsockname for musl

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