Use fallback engine for as the non-temporal engine for unknown CPU types

Using the non-temporal AVX engine for unknown CPU types looks like a mistake to
me, and the default built into the switch case is to use the fallback engine. I
don't think this is causing issues now, but it might once we add ARM support.

PiperOrigin-RevId: 561097994
Change-Id: I7f0edd447017c09acd49e4ea11476e32740d630a

absl/crc/internal/crc_memcpy_x86_64.cc

@@ -348,7 +348,6 @@ CrcMemcpy::ArchSpecificEngines CrcMemcpy::GetArchSpecificEngines() {
   // Get the underlying architecture.
   // Get the underlying architecture.
   CpuType cpu_type = GetCpuType();
   CpuType cpu_type = GetCpuType();
   switch (cpu_type) {
   switch (cpu_type) {
-    case CpuType::kUnknown:
     case CpuType::kAmdRome:
     case CpuType::kAmdRome:
     case CpuType::kAmdNaples:
     case CpuType::kAmdNaples:
     case CpuType::kIntelCascadelakeXeon:
     case CpuType::kIntelCascadelakeXeon: