[modules] Accept equivalent module caches from different symlink (#90925)

Use `VFS.equivalent()`, which follows symlinks, to check if two module
cache paths are equivalent. This prevents a PCH error when building from
a different path that is a symlink of the original.

```
error: PCH was compiled with module cache path '/home/foo/blah/ModuleCache/2IBP1TNT8OR8D', but the path is currently '/data/users/foo/blah/ModuleCache/2IBP1TNT8OR8D'
1 error generated.
```