- to keep RUST_BACKTRACE=1 enabled during build, properly separate
MAKE_ENV and TEST_ENV, by introducing a TEST_BIN variable used to
launch rustbuild with TEST_ENV (some tests are failing if RUST_BACKTRACE
is enabled).
- remove llvm-6 backported patches. this version of rustc has full
support of it. Hashes in library names will change when ports llvm
is upgraded, so PLIST will have to be regenerated.
- backport #49140 to be able to run "make test" without installing rustc