.github: update to Go 1.18.1

Also regenerate all of the stubs, we don't need "+build" anymore
because both Go 1.17 and 1.18 use "go:build" for build tags.

Author: kevinburkesegment

.github/workflows/go.yml

@@ -7,8 +7,8 @@ jobs:
     strategy:
       matrix:
         go:
-        - 1.16
-        - 1.17
+        - 1.17.x
+        - 1.18.x
         os:
         - ubuntu-latest
 
@@ -43,12 +43,9 @@ jobs:
     - name: Setup Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.17.x
+        go-version: 1.18.x
 
-    - name: Generate
-      run: make --always-make build
-
-    - name: Git Status
+    - name: Ensure generated assembler code is up to date
       run: |
-        git diff
-        test -z "$(git status --porcelain)"
+        go install github.com/kevinburke/differ@1.2
+        differ make --always-make build

ascii/equal_fold_amd64.go

@@ -1,7 +1,6 @@
 // Code generated by command: go run equal_fold_asm.go -pkg ascii -out ../ascii/equal_fold_amd64.s -stubs ../ascii/equal_fold_amd64.go. DO NOT EDIT.
 
 //go:build !purego
-// +build !purego
 
 #include "textflag.h"
 

ascii/equal_fold_amd64.s

@@ -1,7 +1,6 @@
 // Code generated by command: go run valid_asm.go -pkg ascii -out ../ascii/valid_amd64.s -stubs ../ascii/valid_amd64.go. DO NOT EDIT.
 
 //go:build !purego
-// +build !purego
 
 #include "textflag.h"
 

ascii/valid_amd64.go

@@ -1,7 +1,6 @@
 // Code generated by command: go run valid_print_asm.go -pkg ascii -out ../ascii/valid_print_amd64.s -stubs ../ascii/valid_print_amd64.go. DO NOT EDIT.
 
 //go:build !purego
-// +build !purego
 
 #include "textflag.h"
 

ascii/valid_amd64.s

@@ -1,7 +1,6 @@
 // Code generated by command: go run decode_asm.go -pkg base64 -out ../base64/decode_amd64.s -stubs ../base64/decode_amd64.go. DO NOT EDIT.
 
 //go:build !purego
-// +build !purego
 
 #include "textflag.h"