Fix COMPILER_RT_DEBUG build for targets that don't support thread local storage.

02243993 added code that is only enabled
when COMPILER_RT_DEBUG is enabled. This code doesn't build on targets
that don't support thread local storage because the code added uses the
THREADLOCAL macro. Consequently the COMPILER_RT_DEBUG build broke for
some Apple targets (e.g. 32-bit iOS simulators).

```
/Volumes/user_data/dev/llvm/llvm.org/main/src/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp:216:8: error: thread-local storage is not supported for the current target
static THREADLOCAL InternalDeadlockDetector deadlock_detector;
       ^
/Volumes/user_data/dev/llvm/llvm.org/main/src/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h:227:24: note: expanded from macro 'THREADLOCAL'
 # define THREADLOCAL   __thread
                        ^
1 error generated.
```

To fix this, this patch introduces a `SANITIZER_SUPPORTS_THREADLOCAL`
macro that is `1` iff thread local storage is supported by the current
target. That condition is then added to `SANITIZER_CHECK_DEADLOCKS` to
ensure the code is only enabled when thread local storage is available.

The implementation of `SANITIZER_SUPPORTS_THREADLOCAL` currently assumes
Clang. See `llvm-project/clang/include/clang/Basic/Features.def` for the
definition of the `tls` feature.

rdar://81543007

Differential Revision: https://reviews.llvm.org/D107524