Miri flag passing changed

[RalfJung]

cargo miri test changed to be more compatible with cargo test, but this means we had to find a different way to pass flags to the interpreter, so there now is a MIRIFLAGS environment variable for that. The old way still works for now, but is deprecated.

This affects the following line:

mem-basics/test.sh

Line 20 in 804accc

cargo miri test -p memcpy --target-dir="$MIRI_DIR" -- -Zmiri-disable-isolation

This should now be MIRIFLAGS="-Zmiri-disable-isolation" cargo miri test -p memcpy --target-dir="$MIRI_DIR".

[RalfJung]

Heads-up: I am planning to remove the compatibility hack that made passing Miri flags as cargo arguments still work (rust-lang/miri#1769). Once this lands, CI here will break.