Experimentally add `ffi_const` and `ffi_pure` extern fn attributes#71718

Merged

bors merged 3 commits intorust-lang:masterfrom

neocturne:ffi_const_pure

May 21, 2020

Commits on May 19, 2020

Implement `#[ffi_const]` and `#[ffi_pure]` function attributes
neocturne
committed
Add tests for `#[ffi_const]` and `#[ffi_pure]` function attributes
neocturne
committed
Document `#[ffi_const]` and `#[ffi_pure]` function attributes in unstable book
neocturne
committed