Upgrade blevesearch to v0.8.1 (#9177)

For #1441

a91b427b59

vendor/github.com/RoaringBitmap/roaring/clz_compat.go

@@ -0,0 +1,36 @@
+// +build !go1.9
+
+package roaring
+
+// LeadingZeroBits returns the number of consecutive most significant zero
+// bits of x.
+func countLeadingZeros(i uint64) int {
+	if i == 0 {
+		return 64
+	}
+	n := 1
+	x := uint32(i >> 32)
+	if x == 0 {
+		n += 32
+		x = uint32(i)
+	}
+	if (x >> 16) == 0 {
+		n += 16
+		x <<= 16
+	}
+	if (x >> 24) == 0 {
+		n += 8
+		x <<= 8
+	}
+	if x>>28 == 0 {
+		n += 4
+		x <<= 4
+	}
+	if x>>30 == 0 {
+		n += 2
+		x <<= 2
+
+	}
+	n -= int(x >> 31)
+	return n
+}