cmd/go/internal/modload: fix use of //go:linkname

I can't find the exact rule about space before compiler directive
openings from
https://golang.org/cmd/compile/#hdr-Compiler_Directives
but it seems like the compiler doesn't recognize it
as a compiler directive if it is preceded by space.
Removing the space made the //go:linkname in the __gomod__.go file
working as intended.

Manually tested.

Update #26404

Change-Id: I589f7203a628b2fa6238d82878029e0f098091b6
Reviewed-on: https://go-review.googlesource.com/c/143977
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/internal/modload/build.go

@@ -239,13 +239,10 @@ func ModInfoProg(info string) []byte {
 	// Populate it in an init func so that it will work with go:linkname,
 	// but use a string constant instead of the name 'string' in case
 	// package main shadows the built-in 'string' with some local declaration.
-	return []byte(fmt.Sprintf(`
-		package main
-		import _ "unsafe"
-		//go:linkname __debug_modinfo__ runtime/debug.modinfo
-		var __debug_modinfo__ = ""
-		func init() {
-			__debug_modinfo__ = %q
-		}
+	return []byte(fmt.Sprintf(`package main
+import _ "unsafe"
+//go:linkname __debug_modinfo__ runtime/debug.modinfo
+var __debug_modinfo__ = ""
+func init() { __debug_modinfo__ = %q }
 	`, string(infoStart)+info+string(infoEnd)))
 }