Revert "env/darwin/aws: reduce guest CPU count to 4"

This reverts CL 461775. That CL failed to update cmd/runqemubuildlet,
which is used for production VM execution. Thus it had no impact. The
next CL will change memory, so just revert this for now rather than
fixing to avoid changing two things at once.

For golang/go#48945.
For golang/go#59634.

Change-Id: I9f1e26f2b3ffd6caca9683242a44597b7f1d8d58
Reviewed-on: https://go-review.googlesource.com/c/build/+/484746
Run-TryBot: Michael Pratt <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Commit-Queue: Michael Pratt <[email protected]>

Author: prattmic

env/darwin/aws/qemu.sh

@@ -23,10 +23,9 @@ args=(
   -cpu host
   -machine q35
   -usb -device usb-kbd -device usb-tablet
-  # QEMU scales poorly with CPU count on macOS (see
-  # https://go.dev/issue/48945#issuecomment-1378850381). Increasing CPU count
-  # also increases boot time.
-  -smp cpus=4
+  # macOS only likes a power-of-two number of cores, but odd socket count is
+  # fine.
+  -smp cpus=6,sockets=3,cores=2,threads=1
   -device usb-ehci,id=ehci
   -device nec-usb-xhci,id=xhci
   -global nec-usb-xhci.msi=off