go/build: improve comment on Context.CgoEnabled

Fixes #25953

Change-Id: I4f3a64b42fce76cc5ea6cfe2888d103c7423457d
Reviewed-on: https://go-review.googlesource.com/c/126736Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/go/build/build.go

@@ -34,7 +34,7 @@ type Context struct {
 	GOOS        string // target operating system
 	GOROOT      string // Go root
 	GOPATH      string // Go path
-	CgoEnabled  bool   // whether cgo can be used
+	CgoEnabled  bool   // whether cgo files are included
 	UseAllFiles bool   // use files regardless of +build lines, file names
 	Compiler    string // compiler to assume when computing target paths