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

[delcypher]

Summary

022439931f5be77efaf80b44d587666b0c9b13b5 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

compiler-rt/lib/sanitizer_common/sanitizer_mutex.h

enum {
   // but no other mutex can be locked while under a leaf mutex.
   MutexLeaf = -1,
   // Multiple mutexes of this type can be locked at the same time.
   MutexMulti = -3,
 };
 
 // Go linker does not support THREADLOCAL variables,
 // so we can't use per-thread state.
-#define SANITIZER_CHECK_DEADLOCKS (SANITIZER_DEBUG && !SANITIZER_GO)
+#define SANITIZER_CHECK_DEADLOCKS \
+  (SANITIZER_DEBUG && !SANITIZER_GO && SANITIZER_SUPPORTS_THREADLOCAL)
 
 #if SANITIZER_CHECK_DEADLOCKS
 struct MutexMeta {
   MutexType type;
   const char *name;
   // The table fixes what mutexes can be locked under what mutexes.
   // If the entry for MutexTypeFoo contains MutexTypeBar,
   // then Bar mutex can be locked while under Foo mutex.

compiler-rt/lib/sanitizer_common/sanitizer_platform.h

 // compatible with the sanitizer library being loaded via
 // `dlopen()`.
 #if SANITIZER_MAC
 #define SANITIZER_SUPPORTS_INIT_FOR_DLOPEN 1
 #else
 #define SANITIZER_SUPPORTS_INIT_FOR_DLOPEN 0
 #endif
 
+// SANITIZER_SUPPORTS_THREADLOCAL
+// 1 - THREADLOCAL macro is supported by target
+// 0 - THREADLOCAL macro is not supported by target
+#ifndef __has_feature
+// TODO: Support other compilers here
+#  define SANITIZER_SUPPORTS_THREADLOCAL 1
+#else
+#  if __has_feature(tls)
+#    define SANITIZER_SUPPORTS_THREADLOCAL 1
+#  else
+#    define SANITIZER_SUPPORTS_THREADLOCAL 0
+#  endif
+#endif
+
 #endif // SANITIZER_PLATFORM_H