cmd/compile/internal/gc: rewrite comment to avoid automated meaning

The comment says 'DΟ NΟT SUBMIT', and that text being in a file can cause
automated errors or warnings when trying to check the Go sources into other
source control systems.

(We reject that string in CL commit messages, which I've avoided here
by changing the O's to Ο's above.)

Change-Id: I6cdd57a8612ded5208f05a8bd6b137f44424a030
Reviewed-on: https://go-review.googlesource.com/22434
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/bexport.go

@@ -121,7 +121,7 @@ const debugFormat = false // default: false
 const posInfoFormat = false
 
 // TODO(gri) remove eventually
-const forceNewExport = false // force new export format - DO NOT SUBMIT with this flag set
+const forceNewExport = false // force new export format - do NOT submit with this flag set
 
 // forceObjFileStability enforces additional constraints in export data
 // and other parts of the compiler to eliminate object file differences