Add another path where a Rosetta 2 daemon plist file is possibly located

[yvt]

This PR fixes Rosetta 2 detection on macOS 11.5.0 and later.

#4310 updated Settings::getDefaultExtraPlatforms to detect the presence of Rosetta 2 and include x86_64-darwin automatically when eligible. It does so by checking the existence of a file at /Library/Apple/System/Library/LaunchDaemons/com.apple.oahd.plist. However, as of macOS 11.5.0, this detection method stopped working because the file is now located in a different path /System/Library/LaunchDaemons/com.apple.oahd.plist. This PR introduces a check for this new path to fix this issue.

[roberth]

This change has added x86_64-darwin to my machine, but when I build an x86_64-darwin derivation, it fails without an error message (although the lack of a message may be due to a low level exception handling bug that I'm fixing). When I invoke an intel executable manually, I get a "bad file descriptor" error.
I did not enable Rosetta on the machine; I've only installed nix and then nix-darwin on it.

I use an M1 with

> sw_vers                                                                                                                                                                                                                                                                            ~
ProductName:	macOS
ProductVersion:	11.6
BuildVersion:	20G165

it has the a file in the "new" location but it does not have an oahd process.