Support multiple variants for a given llm lib type

In some cases we may want multiple variants for a given GPU type or CPU.
This adds logic to have an optional Variant which we can use to select
an optimal library, but also allows us to try multiple variants in case
some fail to load.

This can be useful for scenarios such as ROCm v5 vs v6 incompatibility
or potentially CPU features.

llm/shim_darwin.go

@@ -2,13 +2,7 @@ package llm
 
 import (
 	"embed"
-	"errors"
 	"fmt"
-	"io"
-	"io/fs"
-	"log"
-	"os"
-	"path/filepath"
 
 	"github.com/jmorganca/ollama/api"
 )
@@ -20,52 +14,3 @@ func newDynamicShimExtServer(library, model string, adapters, projectors []strin
 	// should never happen...
 	return nil, fmt.Errorf("Dynamic library loading not supported on Mac")
 }
-
-func nativeInit(workdir string) error {
-	err := extractPayloadFiles(workdir, "llama.cpp/ggml-metal.metal")
-	if err != nil {
-		if err == payloadMissing {
-			// TODO perhaps consider this a hard failure on arm macs?
-			log.Printf("ggml-meta.metal payload missing")
-			return nil
-		}
-		return err
-	}
-	os.Setenv("GGML_METAL_PATH_RESOURCES", workdir)
-	return nil
-}
-
-func extractPayloadFiles(workDir, glob string) error {
-	files, err := fs.Glob(libEmbed, glob)
-	if err != nil || len(files) == 0 {
-		return payloadMissing
-	}
-
-	for _, file := range files {
-		srcFile, err := libEmbed.Open(file)
-		if err != nil {
-			return fmt.Errorf("read payload %s: %v", file, err)
-		}
-		defer srcFile.Close()
-		if err := os.MkdirAll(workDir, 0o755); err != nil {
-			return fmt.Errorf("create payload temp dir %s: %v", workDir, err)
-		}
-
-		destFile := filepath.Join(workDir, filepath.Base(file))
-		_, err = os.Stat(destFile)
-		switch {
-		case errors.Is(err, os.ErrNotExist):
-			destFile, err := os.OpenFile(destFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o755)
-			if err != nil {
-				return fmt.Errorf("write payload %s: %v", file, err)
-			}
-			defer destFile.Close()
-			if _, err := io.Copy(destFile, srcFile); err != nil {
-				return fmt.Errorf("copy payload %s: %v", file, err)
-			}
-		case err != nil:
-			return fmt.Errorf("stat payload %s: %v", file, err)
-		}
-	}
-	return nil
-}