Auto merge of #31668 - cuviper:lfs, r=alexcrichton
Auto merge of #31668 - cuviper:lfs, r=alexcrichton

This follows the pattern already used for stat functions from #31551.  Now
`ftruncate`, `lseek`, and `readdir_r` use their explicit 64-bit variants for
LFS support, using wider `off_t` and `dirent` types.  This also updates to
`open64`, which uses no different types but implies the `O_LARGEFILE` flag.

Non-Linux platforms just map their normal functions to the 64-bit names.

r? @alexcrichton

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