Merge remote-tracking branch 'remotes/thuth-gitlab/tags/s390-ccw-bios-2021-05-10' into staging

* Make the s390-ccw bios compilable with Clang
* Fix ECKD booting with null block numbers in the chain

# gpg: Signature made Mon 10 May 2021 08:27:34 BST
# gpg:                using RSA key 27B88847EEE0250118F3EAB92ED9D774FE702DB5
# gpg:                issuer "thuth@redhat.com"
# gpg: Good signature from "Thomas Huth <th.huth@gmx.de>" [full]
# gpg:                 aka "Thomas Huth <thuth@redhat.com>" [full]
# gpg:                 aka "Thomas Huth <huth@tuxfamily.org>" [full]
# gpg:                 aka "Thomas Huth <th.huth@posteo.de>" [unknown]
# Primary key fingerprint: 27B8 8847 EEE0 2501 18F3  EAB9 2ED9 D774 FE70 2DB5

* remotes/thuth-gitlab/tags/s390-ccw-bios-2021-05-10:
  pc-bios/s390: Update the s390-ccw bios binaries with the Clang and other fixes
  pc-bios/s390-ccw: Allow building with Clang, too
  pc-bios/s390-ccw: Silence GCC 11 stringop-overflow warning
  pc-bios/s390-ccw: Fix the cc-option macro in the Makefile
  pc-bios/s390-ccw: Silence warning from Clang by marking panic() as noreturn
  pc-bios/s390-ccw/netboot: Use "-Wl," prefix to pass parameter to the linker
  pc-bios/s390-ccw: Use reset_psw pointer instead of hard-coded null pointer
  pc-bios/s390-ccw/bootmap: Silence compiler warning from Clang
  pc-bios/s390-ccw: don't try to read the next block if end of chunk is reached

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