git: fix error wrapping to ensure internal errors are propogated

Also, tidy up the error printing, so that now we always print out the
"current commit information was not captured by the build" message,
instead of just for not locating the git binary.

Before:

	WARNING: buildx: git was not found in the system. Current commit information was not captured by the build

After:

	WARNING: current commit information was not captured by the build: git was not found in the system: <error message>

Signed-off-by: Justin Chadwell <me@jedevc.com>

Author: jedevc

build/build.go

@@ -737,7 +737,7 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 		hasMobyDriver := false
 		gitattrs, err := getGitAttributes(ctx, opt.Inputs.ContextPath, opt.Inputs.DockerfilePath)
 		if err != nil {
-			logrus.Warn(err)
+			logrus.WithError(err).Warn("current commit information was not captured by the build")
 		}
 		for i, np := range m[k] {
 			node := nodes[np.driverIndex]

build/git.go

@@ -51,21 +51,21 @@ func getGitAttributes(ctx context.Context, contextPath string, dockerfilePath st
 
 	gitc, err := gitutil.New(gitutil.WithContext(ctx), gitutil.WithWorkingDir(wd))
 	if err != nil {
-		if st, err := os.Stat(path.Join(wd, ".git")); err == nil && st.IsDir() {
-			return res, errors.New("buildx: git was not found in the system. Current commit information was not captured by the build")
+		if st, err1 := os.Stat(path.Join(wd, ".git")); err1 == nil && st.IsDir() {
+			return res, errors.Wrap(err, "git was not found in the system")
 		}
 		return
 	}
 
 	if !gitc.IsInsideWorkTree() {
 		if st, err := os.Stat(path.Join(wd, ".git")); err == nil && st.IsDir() {
-			return res, errors.New("buildx: failed to read current commit information with git rev-parse --is-inside-work-tree")
+			return res, errors.New("failed to read current commit information with git rev-parse --is-inside-work-tree")
 		}
 		return res, nil
 	}
 
 	if sha, err := gitc.FullCommit(); err != nil && !gitutil.IsUnknownRevision(err) {
-		return res, errors.Wrapf(err, "buildx: failed to get git commit")
+		return res, errors.Wrap(err, "failed to get git commit")
 	} else if sha != "" {
 		checkDirty := false
 		if v, ok := os.LookupEnv("BUILDX_GIT_CHECK_DIRTY"); ok {
@@ -95,7 +95,7 @@ func getGitAttributes(ctx context.Context, contextPath string, dockerfilePath st
 
 	if setGitLabels {
 		if root, err := gitc.RootDir(); err != nil {
-			return res, errors.Wrapf(err, "buildx: failed to get git root dir")
+			return res, errors.Wrap(err, "failed to get git root dir")
 		} else if root != "" {
 			if dockerfilePath == "" {
 				dockerfilePath = filepath.Join(wd, "Dockerfile")