Reapply r355803 (by mmel):

Fix LLVM libunwnwind _Unwind_Backtrace symbol version for ARM.
In original  GNU libgcc, _Unwind_Backtrace is published with GCC_3.3 version
for all architectures but ARM. For ARM should be publishes with GCC_4.3.0
version. This was originally omitted in r255095, fixed in r318024 and omitted
aging in LLVM libunwind implementation in r354347.

For ARM _Unwind_Backtrace should be published as default with GCC_4.3.0
version , (because this is right original version) and again as
normal(not-default) with GCC_3.3 version (to maintain ABI compatibility
compiled/linked with wrong pre r318024 libgcc)

PR:	233664

contrib/llvm-project/libunwind/src/UnwindLevel1-gcc-ext.c

@@ -181,6 +181,10 @@ _Unwind_Backtrace(_Unwind_Trace_Fn callback, void *ref) {
     }
   }
 }
+#ifdef __arm__
+/* Preserve legacy libgcc (pre r318024) ARM ABI mistake */
+__sym_compat(_Unwind_Backtrace, _Unwind_Backtrace, GCC_3.3);
+#endif
 
 
 /// Find DWARF unwind info for an address 'pc' in some function.