Add EnableFsyncGitDir to enable synchronized writes to the gitdir (#874)

This adds support for the GIT_OPT_ENABLE_FSYNC_GITDIR option in libgit2.

Co-authored-by: James Fargher <jfargher@gitlab.com>
(cherry picked from commit 1fcc9d8)

settings.go

@@ -101,6 +101,14 @@ func EnableStrictHashVerification(enabled bool) error {
 	}
 }
 
+func EnableFsyncGitDir(enabled bool) error {
+	if enabled {
+		return setSizet(C.GIT_OPT_ENABLE_FSYNC_GITDIR, 1)
+	} else {
+		return setSizet(C.GIT_OPT_ENABLE_FSYNC_GITDIR, 0)
+	}
+}
+
 func CachedMemory() (current int, allowed int, err error) {
 	return getSizetSizet(C.GIT_OPT_GET_CACHED_MEMORY)
 }

settings_test.go

@@ -65,6 +65,14 @@ func TestEnableStrictHashVerification(t *testing.T) {
 	checkFatal(t, err)
 }
 
+func TestEnableFsyncGitDir(t *testing.T) {
+	err := EnableFsyncGitDir(false)
+	checkFatal(t, err)
+
+	err = EnableFsyncGitDir(true)
+	checkFatal(t, err)
+}
+
 func TestCachedMemory(t *testing.T) {
 	current, allowed, err := CachedMemory()
 	checkFatal(t, err)