[TSan] Align thread_registry_placeholder

s390x requires ThreadRegistry.mtx_.opaque_storage_ to be 4-byte
aligned. Since other architectures may have similar requirements, use
the maximum thread_registry_placeholder alignment from other
sanitizers, which is 64 (LSan).

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D105629

compiler-rt/lib/tsan/rtl/tsan_rtl.cpp

@@ -77,7 +77,7 @@ void OnInitialize() {
 }
 #endif
 
-static char thread_registry_placeholder[sizeof(ThreadRegistry)];
+static ALIGNED(64) char thread_registry_placeholder[sizeof(ThreadRegistry)];
 
 static ThreadContextBase *CreateThreadContext(u32 tid) {
   // Map thread trace when context is created.