Ignore go:linkname directives in the internal/fuzz package.

All they do is insert fuzzing implementation stubs into the runtime
package, which our runtime doesn't use anyway. The stubs should be
discarded by dead code elimination automatically, so there is no
disadvantage compared to excluding the original source file.

Author: nevkontakte

compiler/linkname.go

@@ -116,7 +116,7 @@ func parseGoLinknames(fset *token.FileSet, pkgPath string, file *ast.File) ([]Go
 
 		decl := obj.Decl.(*ast.FuncDecl)
 		if decl.Body != nil {
-			if pkgPath == "runtime" || pkgPath == "internal/bytealg" {
+			if pkgPath == "runtime" || pkgPath == "internal/bytealg" || pkgPath == "internal/fuzz" {
 				// These standard library packages are known to use unsupported
 				// "insert"-style go:linkname directives, which we ignore here and handle
 				// case-by-case in native overrides.