Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-tcg-20210726' into staging

Fix icount accounting.
Replace bitrev8 with revbit8.
Fixes for set but not used warnings.

# gpg: Signature made Mon 26 Jul 2021 22:45:37 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-gitlab/tags/pull-tcg-20210726:
  tests/unit: Remove unused variable from test_io
  linux-user/syscall: Remove unused variable from execve
  hw/pci-hist/pnv_phb4: Fix typo in pnv_phb4_ioda_write
  hw/ppc/spapr_events: Remove unused variable from check_exception
  hw/audio/adlib: Remove unused variable in adlib_callback
  net/checksum: Remove unused variable in net_checksum_add_iov
  util/selfmap: Discard mapping on error
  accel/tcg: Remove unused variable in cpu_exec
  nbd/server: Mark variable unused in nbd_negotiate_meta_queries
  bitops.h: revert db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation")
  accel/tcg: Remove unnecessary check on icount_extra in cpu_loop_exec_tb()
  accel/tcg: Don't use CF_COUNT_MASK as the max value of icount_decr.u16.low

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