[libunwind] Only include cet.h if __CET__ defined

We should not assume that the cet.h header exists just because
we're on x86 linux. Only include it if __CET__ is defined. This
makes the code more similar to what compiler-rt does in
https://github.com/llvm/llvm-project/blob/ee423d93ead39e94c2970b3cc7ef6e6faa75d10b/compiler-rt/lib/builtins/assembly.h#L17
(though that one also has a __has_include() check -- I've not found
that to be necessary).

Differential Revision: https://reviews.llvm.org/D119697

GitOrigin-RevId: 2d2ef384b2f6e723edb793d08f52e7f4dc94ba3a
1 file changed
tree: 05e8e93a8ef65930c9bf3f49e54c886e16bad6d5
  1. cmake/
  2. docs/
  3. include/
  4. src/
  5. test/
  6. .clang-format
  7. CMakeLists.txt
  8. LICENSE.TXT