[libunwind][cmake] Compile _Unwind* routines with -fexceptions

libunwind/src/CMakeLists.txt

@@ -20,7 +20,12 @@ set(LIBUNWIND_C_SOURCES
     )
 set_source_files_properties(${LIBUNWIND_C_SOURCES}
                             PROPERTIES
-                              COMPILE_FLAGS "-std=c99")
+                              # We need to set `-fexceptions` here so that key
+                              # unwinding functions, like
+                              # _UNWIND_RaiseException, are not marked as
+                              # `nounwind`, which breaks LTO builds of
+                              # libunwind.  See #56825 and #120657 for context.
+                              COMPILE_FLAGS "-std=c99 -fexceptions")
 
 set(LIBUNWIND_ASM_SOURCES
     UnwindRegistersRestore.S