rust-target-config: Add has-thread-local option

rust-target-config: Add has-thread-local option

The "has-elf-tls" option was removed by the commit
8e1614a906086fb46c5dd7b7f2dffab91194165c. However is should have been
renamed to "has-thread-local", since it was renamed and not removed in
rust by this commit.
https://github.com/rust-lang/rust/commit/391332c5d9d5a5e97a0d36e011a87ad43045cfd3

Signed-off-by: Per x Johansson <perxjoh@axis.com>
Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>