Detect lack of AVX and fallback to CPU mode

We build the GPU libraries with AVX enabled to ensure that if not all
layers fit on the GPU we get better performance in a mixed mode.
If the user is using a virtualization/emulation system that lacks AVX
this used to result in an illegal instruction error and crash before this
fix.  Now we will report a warning in the server log, and just use
CPU mode to ensure we don't crash.

gpu/gpu.go

@@ -122,9 +122,15 @@ func GetGPUInfo() GpuInfo {
 		initGPUHandles()
 	}
 
+	// All our GPU builds have AVX enabled, so fallback to CPU if we don't detect at least AVX
+	cpuVariant := GetCPUVariant()
+	if cpuVariant == "" {
+		slog.Warn("CPU does not have AVX or AVX2, disabling GPU support.")
+	}
+
 	var memInfo C.mem_info_t
 	resp := GpuInfo{}
-	if gpuHandles.cuda != nil {
+	if gpuHandles.cuda != nil && cpuVariant != "" {
 		C.cuda_check_vram(*gpuHandles.cuda, &memInfo)
 		if memInfo.err != nil {
 			slog.Info(fmt.Sprintf("error looking up CUDA GPU memory: %s", C.GoString(memInfo.err)))
@@ -143,7 +149,7 @@ func GetGPUInfo() GpuInfo {
 				slog.Info(fmt.Sprintf("CUDA GPU is too old. Falling back to CPU mode. Compute Capability detected: %d.%d", cc.major, cc.minor))
 			}
 		}
-	} else if gpuHandles.rocm != nil {
+	} else if gpuHandles.rocm != nil && cpuVariant != "" {
 		C.rocm_check_vram(*gpuHandles.rocm, &memInfo)
 		if memInfo.err != nil {
 			slog.Info(fmt.Sprintf("error looking up ROCm GPU memory: %s", C.GoString(memInfo.err)))
@@ -185,7 +191,7 @@ func GetGPUInfo() GpuInfo {
 	if resp.Library == "" {
 		C.cpu_check_ram(&memInfo)
 		resp.Library = "cpu"
-		resp.Variant = GetCPUVariant()
+		resp.Variant = cpuVariant
 	}
 	if memInfo.err != nil {
 		slog.Info(fmt.Sprintf("error looking up CPU memory: %s", C.GoString(memInfo.err)))