Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2020-01-14' into staging

Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2020-01-14' into staging

QAPI patches for 2020-01-14

# gpg: Signature made Tue 14 Jan 2020 10:15:22 GMT
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2020-01-14:
  qapi: Simplify QAPISchemaModularCVisitor
  qapi: Fix code generation for empty modules
  qapi: Proper intermediate representation for modules
  qapi: Generate command registration stuff into separate files
  tests/Makefile.include: Fix missing test-qapi-emit-events.[ch]
  qapi: Tweak "command returns a nice type" check for clarity

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