all: build tags: appengine,!gccgo => purego,gc

appengine is obsolete and superseded by purego, and gc is a more
precise tag for files that use gc-syntax assembly.

Change-Id: I716f59de772ebeee4adf4d2a432edf300122cef0
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/269920
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>

sha3/hashes_generic.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build gccgo appengine !s390x
+// +build !gc purego !s390x
 
 package sha3
 

sha3/keccakf.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//  +build !amd64 appengine gccgo
+//  +build !amd64 purego !gc
 
 package sha3
 

sha3/keccakf_amd64.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64,!appengine,!gccgo
+// +build amd64,!purego,gc
 
 package sha3
 

sha3/keccakf_amd64.s

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64,!appengine,!gccgo
+// +build amd64,!purego,gc
 
 // This code was translated into a form compatible with 6a from the public
 // domain sources at https://github.com/gvanas/KeccakCodePackage

sha3/sha3_s390x.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !gccgo,!appengine
+// +build gc,!purego
 
 package sha3
 

sha3/sha3_s390x.s

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !gccgo,!appengine
+// +build gc,!purego
 
 #include "textflag.h"
 

sha3/shake_generic.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build gccgo appengine !s390x
+// +build !gc purego !s390x
 
 package sha3
 

sha3/xor.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64,!386,!ppc64le appengine
+// +build !amd64,!386,!ppc64le purego
 
 package sha3
 

sha3/xor_unaligned.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build amd64 386 ppc64le
-// +build !appengine
+// +build !purego
 
 package sha3