Fix a warning and an uninitialized variable in benchmark (#200927)
After #198964 I see a -Wcovered-switch-default warning in sysinfo.cc,
but it looks like it's uncovering something a bit worse.
Back in #147357 and #149159 it looks like we tried to fix an MSVC
warning for an uncovered `CacheUnknown` case in this switch, and removed
the initialization of the variable before the switch. The update to
Google Benchmark v1.9.5 has a different fix for this - it's handling
that specific case guarded by some MSVC version macros, but this depends
on the initialization we removed!
Add the initialization back and remove the default case, effectively
reverting #149159 and #147357.
llvm-project
1fe6d564 - Fix a warning and an uninitialized variable in benchmark (#200927)
