Stop using deprecated "-Z" rustc-flag to reduce Travis Spam

[juleskers]

I just checked the Travis logs because my PR didn't build, and was greeted, among others, with 266 copies of

warning: the option Z is unstable and should only be used on the nightly compiler, but it is currently accepted for backwards compatibility; this will soon change, see issue #31847 for more details

The warning references RustC issue #31847, which says we shouldn't pass unstable debug flags to stable compilers.

The rust-by-example makefile specifies -Z no-trans, I presume for speed reasons?
Is this something that should maybe be reconsidered?

[steveklabnik]

The rust-by-example makefile specifies -Z no-trans, I presume for speed reasons?
Is this something that should maybe be reconsidered?

yes, it should be cargo check now instead.

In genearl all of the RBE build stuff is very out of date :/

[titanous]

I think this was fixed by #872.

[juleskers]

Jup, it was! Thanks for paying attention!