salsa20/salsa: fix amd64 assembly not to smash SP

**salsa20 is used by V1 protocol of DNSCrypt** golang/go#44269 quote: x/crypto/*.s masks and writes to SP during function execution. This is not allowed by the Go ABI. All SP modifications on goroutine stacks must be constant additions or subtractions, or else the garbage collector cannot unwind the stack from that location. Code used to get away with this due to cooperative scheduling, but now that we scan stacks preemptively, it is especially important that functions not do this. New code in Go 1.17 will stop stack traces in such functions, which will make programs crash more loudly. But they are still broken in earlier versions and may just cause silent memory corruption instead of loud crashes. hashBlocksSSE2 and hashBlocksSSSE3 should leave SP alone.
AZ-X · Feb 20, 2021 · 9e9751d · 9e9751d
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diff --git a/go.mod b/go.mod
@@ -8,7 +8,7 @@ require (
 	github.com/jedisct1/dlog v0.0.0-20190909160351-692385b00b84
 	github.com/jedisct1/go-clocksmith v0.0.0-20190707124905-73e087c7979c
 	github.com/miekg/dns v1.1.35
-	golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9
+	golang.org/x/crypto v0.0.0-20210220033148-5ea612d1eb83
 	golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a
 	gopkg.in/natefinch/lumberjack.v2 v2.0.0
 	stammel v0.0.0-00010101000000-000000000000

diff --git a/vendor/golang.org/x/crypto/salsa20/salsa/salsa20_amd64.go b/vendor/golang.org/x/crypto/salsa20/salsa/salsa20_amd64.go