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.