startCloudQEMU hardcoded -machine q35,accel=kvm and -cpu host,
which fails on any host without KVM (notably macOS). Replace
with a qemuAccelArgs helper that probes /dev/kvm and falls back
to QEMU's TCG software emulation, matching the pattern already
used by tstest/integration/nat. Also wire the helper into
startGokrazyQEMU so gokrazy VMs pick up KVM when available.
Updates #13038
Change-Id: I7745518db823279b1880957bb14ca2ffdaab4c50
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad Fitzpatrick
f4c5613156