Building with rust 1.48 with warnings as errors (i.e. automation) fails with:

error: attribute should be applied to a function or static
   --> toolkit/mozapps/defaultagent/rust/src/lib.rs:111:5
    | 
111 |     #[no_mangle]
    |     ^^^^^^^^^^^^
112 |     static gWinEventLogSourceName: *const u16; 
    |     ------------------------------------------ not a function or static
    | 
    = note: `-D unused-attributes` implied by `-D warnings`
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
error: aborting due to previous error

https://hg.mozilla.org/mozilla-central/rev/52c68bee8952