Use build tags to generate accelerated binaries for CUDA and ROCm on Linux.

The build tags rocm or cuda must be specified to both go generate and go build.
ROCm builds should have both ROCM_PATH set (and the ROCM SDK present) as well
as CLBlast installed (for GGML) and CLBlast_DIR set in the environment to the
CLBlast cmake directory (likely /usr/lib/cmake/CLBlast). Build tags are also
used to switch VRAM detection between cuda and rocm implementations, using
added "accelerator_foo.go" files which contain architecture specific functions
and variables. accelerator_none is used when no tags are set, and a helper
function addRunner will ignore it if it is the chosen accelerator. Fix go
generate commands, thanks @deadmeu for testing.

llm/accelerator_cuda.go

@@ -0,0 +1,67 @@
+//go:build cuda
+
+package llm
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"log"
+	"os/exec"
+	"path"
+	"strconv"
+	"strings"
+
+	"github.com/jmorganca/ollama/format"
+)
+
+var (
+	errNvidiaSMI     = errors.New("warning: gpu support may not be enabled, check that you have installed GPU drivers: nvidia-smi command failed")
+	errAvailableVRAM = errors.New("not enough VRAM available, falling back to CPU only")
+)
+
+// acceleratedRunner returns the runner for this accelerator given the provided buildPath string.
+func acceleratedRunner(buildPath string) []ModelRunner {
+	return []ModelRunner{
+		ModelRunner{
+			Path:        path.Join(buildPath, "cuda", "bin", "ollama-runner"),
+			Accelerated: true,
+		},
+	}
+}
+
+// CheckVRAM returns the free VRAM in bytes on Linux machines with NVIDIA GPUs
+func CheckVRAM() (int64, error) {
+	cmd := exec.Command("nvidia-smi", "--query-gpu=memory.free", "--format=csv,noheader,nounits")
+	var stdout bytes.Buffer
+	cmd.Stdout = &stdout
+	err := cmd.Run()
+	if err != nil {
+		return 0, errNoAccel
+	}
+
+	var freeMiB int64
+	scanner := bufio.NewScanner(&stdout)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.Contains(line, "[Insufficient Permissions]") {
+			return 0, fmt.Errorf("GPU support may not enabled, check you have installed GPU drivers and have the necessary permissions to run nvidia-smi")
+		}
+
+		vram, err := strconv.ParseInt(strings.TrimSpace(line), 10, 64)
+		if err != nil {
+			return 0, fmt.Errorf("failed to parse available VRAM: %v", err)
+		}
+
+		freeMiB += vram
+	}
+
+	freeBytes := freeMiB * 1024 * 1024
+	if freeBytes < 2*format.GigaByte {
+		log.Printf("less than 2 GB VRAM available")
+		return 0, errAvailableVRAM
+	}
+
+	return freeBytes, nil
+}