Revert "[AddressSanitizer] Don't use weak linkage for __{start,stop}_asan_globals"

This reverts commit d76e62fd.

Reverting since this can lead to linker errors:

```
ld.lld: error: undefined hidden symbol: __start_asan_globals
```

when using --gc-sections. The linker can discard __start_asan_globals
once there are no more `asan_globals` sections left, which can lead to
this error if we have external linkages to them.