Rollup merge of #101014 - isikkema:fix-zmeta-stats-file-encoder-no-read-perms, r=isikkema

Fix -Zmeta-stats ICE by giving `FileEncoder` file read permissions

Fixes #101001

As far as I can tell, #101001 is caused because the file is being created with write-only permissions here: https://github.com/rust-lang/rust/blob/master/compiler/rustc_serialize/src/opaque.rs#L196

but it is trying to be read here: https://github.com/rust-lang/rust/blob/master/compiler/rustc_metadata/src/rmeta/encoder.rs#L780

This PR attempts to fix this by creating/opening the file with the same permissions as `File::create()` with the addition of read.

Author: notriddle