[libc++] Move handling of the target triple to the DSL

This fixes a long standing issue where the triple is not always set
consistently in all configurations. This change also moves the
back-deployment Lit features to using the proper target triple
instead of using something ad-hoc.

This will be necessary for using from scratch Lit configuration files
in both normal testing and back-deployment testing.

Differential Revision: https://reviews.llvm.org/D102012

NOKEYCHECK=True
GitOrigin-RevId: 74d096e5587969e0d1458ea2175515f6f02e7df3
1 file changed
tree: d7d8eadf25cc49e7dbb16a1692780b060564be77
  1. .clang-format
  2. CMakeLists.txt
  3. LICENSE.TXT
  4. cmake/
  5. docs/
  6. include/
  7. src/
  8. test/