[PING][PATCH] Fix environment variables restoring in GCC testsuite.

[Mike Stump]

> When I ran Asan test on Asan-bootstrapped GCC, some of them fail with
> memory leaks into GCC, even if Lsan is disabled. This caused by slightly
> wrong logic in saving/restoring env variables functionality in
> gcc-dg.exp (some tests override ASAN_OPTIONS and this env variable isn't
> restored correcty).

> Ok to commit?

Ok.  I’ll note there are 22 other places like this.