[compiler-rt] [UBSan] leave BufferedStackTrace uninit

Otherwise we have to memset 2040 bytes (255 * 8) for each call

Pull Request: #102253

Author: fmayer

compiler-rt/lib/ubsan/ubsan_diag.cpp

@@ -47,7 +47,7 @@ static void MaybePrintStackTrace(uptr pc, uptr bp) {
   if (!flags()->print_stacktrace)
     return;
 
-  BufferedStackTrace stack;
+  UNINITIALIZED BufferedStackTrace stack;
   ubsan_GetStackTrace(&stack, kStackTraceMax, pc, bp, nullptr,
                 common_flags()->fast_unwind_on_fatal);
   stack.Print();

compiler-rt/lib/ubsan/ubsan_diag_standalone.cpp

@@ -29,7 +29,7 @@ extern "C" {
 SANITIZER_INTERFACE_ATTRIBUTE
 void __sanitizer_print_stack_trace() {
   GET_CURRENT_PC_BP;
-  BufferedStackTrace stack;
+  UNINITIALIZED BufferedStackTrace stack;
   stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_fatal);
   stack.Print();
 }