Align to the purego build tag, removing noasm build tag

The `purego` build tag has been proposed[1] as the de-facto tag for
pure Go builds. This is a superset of the `noasm` tag currently used.

This patch aligns the code base to toggle to pure Go implementation
when `purego` is defined.

Verified that all assembly is excluded by doing:

    find . -name '*.s' -exec sed -i -e '$athis-is-not-valid-assembly 12345' {} \;
    go test --tags purego ./...

[1]: golang/go#23172

Makefile

@@ -16,7 +16,7 @@ GOARCH       ?=
 BUILD_ARCH   = $(shell $(GO) env GOARCH)
 
 ifeq ($(NOASM),1)
-	OPTS+=--tags noasm
+	OPTS+=--tags purego
 endif
 
 ifeq ($(V),1)

dh/csidh/fp511_amd64.go

@@ -1,5 +1,5 @@
-//go:build amd64 && !noasm
-// +build amd64,!noasm
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 package csidh
 

dh/csidh/fp511_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 

dh/sidh/internal/p434/arith_amd64.s

@@ -1,4 +1,4 @@
-// +build amd64,!noasm
+// +build amd64,!purego
 
 #include "textflag.h"
 

dh/sidh/internal/p503/arith_amd64.s

@@ -1,4 +1,4 @@
-// +build amd64,!noasm
+// +build amd64,!purego
 
 #include "textflag.h"
 

dh/sidh/internal/p503/arith_arm64.s

@@ -1,4 +1,4 @@
-// +build arm64,!noasm
+// +build arm64,!purego
 
 #include "textflag.h"
 

dh/sidh/internal/p751/arith_amd64.s

@@ -1,4 +1,4 @@
-// +build amd64,!noasm
+// +build amd64,!purego
 
 #include "textflag.h"
 

dh/sidh/internal/p751/arith_arm64.s

@@ -1,4 +1,4 @@
-// +build arm64,!noasm
+// +build arm64,!purego
 
 #include "textflag.h"
 

dh/sidh/internal/templates/arith_decl.gotemp

@@ -1,8 +1,8 @@
 // Code generated by go generate; DO NOT EDIT.
 // This file was generated by robots.
 
-//go:build {{if .OPT_ARM}}({{end}}amd64 && !noasm{{if .OPT_ARM}}) || (arm64 && !noasm){{end}}
-// +build amd64,!noasm{{if .OPT_ARM}} arm64,!noasm{{end}}
+//go:build {{if .OPT_ARM}}({{end}}amd64 && !purego{{if .OPT_ARM}}) || (arm64 && !purego){{end}}
+// +build amd64,!purego{{if .OPT_ARM}} arm64,!purego{{end}}
 
 package {{.PACKAGE}}
 

dh/sidh/internal/templates/arith_generic.gotemp

@@ -1,8 +1,8 @@
 // Code generated by go generate; DO NOT EDIT.
 // This file was generated by robots.
 
-//go:build {{if .OPT_ARM}}noasm || (!amd64 && !arm64){{else}}noasm || !amd64{{end}}
-// +build {{if .OPT_ARM}}noasm !amd64,!arm64{{else}}noasm !amd64{{end}}
+//go:build {{if .OPT_ARM}}purego || (!amd64 && !arm64){{else}}purego || !amd64{{end}}
+// +build {{if .OPT_ARM}}purego !amd64,!arm64{{else}}purego !amd64{{end}}
 
 package {{.PACKAGE}}
 

dh/x25519/curve_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 

dh/x448/curve_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 

ecc/p384/arith.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

ecc/p384/arith_amd64.go

@@ -1,5 +1,5 @@
-//go:build amd64 && !noasm
-// +build amd64,!noasm
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 package p384
 

ecc/p384/arith_amd64.s

@@ -1,4 +1,4 @@
-// +build amd64,!noasm
+// +build amd64,!purego
 
 #include "textflag.h"
 

ecc/p384/arith_arm64.s

@@ -1,4 +1,4 @@
-// +build arm64,!noasm
+// +build arm64,!purego
 
 #include "textflag.h"
 

ecc/p384/arith_test.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

ecc/p384/opt_test.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

ecc/p384/p384_generic.go

@@ -1,5 +1,5 @@
-//go:build noasm || (!amd64 && !arm64)
-// +build noasm !amd64,!arm64
+//go:build purego || (!amd64 && !arm64)
+// +build purego !amd64,!arm64
 
 package p384
 

ecc/p384/p384opt.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

ecc/p384/point.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

ecc/p384/point_test.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

ecc/p384/tableBase.go

@@ -1,5 +1,5 @@
-//go:build (!noasm && arm64) || (!noasm && amd64)
-// +build !noasm,arm64 !noasm,amd64
+//go:build (!purego && arm64) || (!purego && amd64)
+// +build !purego,arm64 !purego,amd64
 
 package p384
 

math/fp25519/fp_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 #include "fp_amd64.h"

math/fp448/fp_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 #include "fp_amd64.h"

pke/kyber/internal/common/amd64.go

@@ -1,5 +1,5 @@
-//go:build amd64
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 package common
 

pke/kyber/internal/common/amd64.s

@@ -1,6 +1,6 @@
 // Code generated by command: go run src.go -out ../amd64.s -stubs ../stubs_amd64.go -pkg common. DO NOT EDIT.
 
-//go:build amd64
+//go:build amd64 && !purego
 
 #include "textflag.h"
 

pke/kyber/internal/common/asm/src.go

@@ -1147,7 +1147,7 @@ func normalizeAVX2() {
 }
 
 func main() {
-	ConstraintExpr("amd64")
+	ConstraintExpr("amd64,!purego")
 
 	addAVX2()
 	subAVX2()

pke/kyber/internal/common/generic.go

@@ -1,5 +1,5 @@
-//go:build !amd64
-// +build !amd64
+//go:build !amd64 || purego
+// +build !amd64 purego
 
 package common
 

sign/dilithium/internal/common/amd64.go

@@ -1,5 +1,5 @@
-//go:build amd64
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 package common
 

sign/dilithium/internal/common/amd64.s

@@ -1,6 +1,6 @@
 // Code generated by command: go run src.go -out ../amd64.s -stubs ../stubs_amd64.go -pkg common. DO NOT EDIT.
 
-//go:build amd64
+//go:build amd64 && !purego
 
 #include "textflag.h"
 

sign/dilithium/internal/common/asm/src.go

@@ -1054,7 +1054,7 @@ func mulBy2toDAVX2() {
 }
 
 func main() {
-	ConstraintExpr("amd64")
+	ConstraintExpr("amd64,!purego")
 
 	nttAVX2()
 	invNttAVX2()

sign/dilithium/internal/common/generic.go

@@ -1,5 +1,5 @@
-//go:build !amd64
-// +build !amd64
+//go:build !amd64 || purego
+// +build !amd64 purego
 
 package common
 

simd/keccakf1600/f1600x2_arm64.go

@@ -1,5 +1,5 @@
-//go:build arm64 && go1.16
-// +build arm64,go1.16
+//go:build arm64 && go1.16 && !purego
+// +build arm64,go1.16,!purego
 
 package keccakf1600
 

simd/keccakf1600/f1600x2_arm64.s

@@ -1,4 +1,4 @@
-// +build arm64,go1.16
+// +build arm64,go1.16,!purego
 
 // Taken from https://github.com/bwesterb/armed-keccak
 

simd/keccakf1600/f1600x4_amd64.go

@@ -1,3 +1,6 @@
+//go:build amd64 && !purego
+// +build amd64,!purego
+
 package keccakf1600
 
 import "github.com/cloudflare/circl/internal/sha3"

simd/keccakf1600/f1600x4_amd64.s

@@ -1,6 +1,6 @@
 // Code generated by command: go run src.go -out ../../f1600x4_amd64.s -stubs ../../f1600x4stubs_amd64.go -pkg keccakf1600. DO NOT EDIT.
 
-//go:build amd64
+//go:build amd64 && !purego
 
 #include "textflag.h"