vendor: update buildkit to 539be170

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/google/uuid/version4.go

@@ -27,6 +27,8 @@ func NewString() string {
 // The strength of the UUIDs is based on the strength of the crypto/rand
 // package.
 //
+// Uses the randomness pool if it was enabled with EnableRandPool.
+//
 // A note about uniqueness derived from the UUID Wikipedia entry:
 //
 //  Randomly generated UUIDs have 122 random bits.  One's annual risk of being
@@ -35,7 +37,10 @@ func NewString() string {
 //  equivalent to the odds of creating a few tens of trillions of UUIDs in a
 //  year and having one duplicate.
 func NewRandom() (UUID, error) {
-	return NewRandomFromReader(rander)
+	if !poolEnabled {
+		return NewRandomFromReader(rander)
+	}
+	return newRandomFromPool()
 }
 
 // NewRandomFromReader returns a UUID based on bytes read from a given io.Reader.
@@ -49,3 +54,23 @@ func NewRandomFromReader(r io.Reader) (UUID, error) {
 	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
 	return uuid, nil
 }
+
+func newRandomFromPool() (UUID, error) {
+	var uuid UUID
+	poolMu.Lock()
+	if poolPos == randPoolSize {
+		_, err := io.ReadFull(rander, pool[:])
+		if err != nil {
+			poolMu.Unlock()
+			return Nil, err
+		}
+		poolPos = 0
+	}
+	copy(uuid[:], pool[poolPos:(poolPos+16)])
+	poolPos += 16
+	poolMu.Unlock()
+
+	uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
+	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
+	return uuid, nil
+}