tune-x86-64-v3.inc: set QEMU_EXTRAOPTIONS like other tune-* files

* use Skylake-Client to match QB_CPU_KVM as changed in:
  https://git.openembedded.org/openembedded-core/commit/?id=6f2af1e5d1537b4d31e14946292bf58f0fd76fc9

* explicitly set -cpu instead of letting qemu to choose based
  on host cpu

* check=false is still useful as e.g. on on AMD Threadripper 3970X:
  orc/0.4.33-r0 $ PSEUDO_UNLOAD=1 qemu-x86_64 -r 3.2.0 -cpu Skylake-Client  -L recipe-sysroot -E LD_LIBRARY_PATH=recipe-sysroot//usr/lib:recipe-sysroot//lib
  orc/0.4.33-r0/build/meson-private/sanitycheckc_cross.exe
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:ECX.x2apic [bit 21]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:ECX.tsc-deadline [bit 24]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.rdseed [bit 18]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.80000001H:ECX.3dnowprefetch [bit 8]
  qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.0DH:EAX.xsavec [bit 1]

* if this still doesn't work for you on your host, you might need to downgrade
  DEFAULTTUNE to e.g. corei7-64 (all all the way back to core2-64), for
  more details see:
  https://www.openembedded.org/pipermail/openembedded-core/2018-April/150178.html



* the leading space shouldn't be needed, I've kept it for consistency
  with other QEMU_EXTRAOPTIONS

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>