Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-tcg-20210107' into staging

Build fix for ppc64 centos7.
Reduce the use of scratch registers for tcg/i386.
Use _aligned_malloc for Win32.
Enable split w^x code gen buffers.

# gpg: Signature made Thu 07 Jan 2021 20:06:38 GMT
# 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-20210107: (47 commits)
  tcg: Constify TCGLabelQemuLdst.raddr
  tcg: Constify tcg_code_gen_epilogue
  tcg: Remove TCG_TARGET_SUPPORT_MIRROR
  tcg/arm: Support split-wx code generation
  tcg/mips: Support split-wx code generation
  tcg/mips: Do not assert on relocation overflow
  accel/tcg: Add mips support to alloc_code_gen_buffer_splitwx_memfd
  tcg/riscv: Support split-wx code generation
  tcg/riscv: Remove branch-over-branch fallback
  tcg/riscv: Fix branch range checks
  tcg/s390: Support split-wx code generation
  tcg/s390: Use tcg_tbrel_diff
  tcg/sparc: Support split-wx code generation
  tcg/sparc: Use tcg_tbrel_diff
  tcg/ppc: Support split-wx code generation
  tcg/ppc: Use tcg_out_mem_long to reset TCG_REG_TB
  tcg/ppc: Use tcg_tbrel_diff
  tcg: Introduce tcg_tbrel_diff
  tcg/tci: Push const down through bytecode reading
  disas: Push const down through host disassembly
  ...

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