compiler: mark global variables whose address is taken

To implement this, change the backend to use flag bits for variables.

Fixes https://gcc.gnu.org/PR100537

Change-Id: I19d803ec3d13003361ea7331cc04297294ec0b8a
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/322129
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
5 files changed