rustc_metadata: Fix unaligned loads
rustc_metadata: Fix unaligned loads

Creating a `&[u32]` from a `&[u8]` was not valid; the data is not
necessarily well aligned.

graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust