backtrace-cpp: implement a better fix for implicit case fallthrough

external/backtrace-cpp/CMakeLists.txt

@@ -38,7 +38,7 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR CMAKE_COMPILER_IS_GNUCXX)
 endif()
 
 # ANBOX: allow old-style casts
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-error=old-style-cast -Wno-error=switch-default -Wno-error=implicit-fallthrough")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-error=old-style-cast -Wno-error=switch-default")
 
 ###############################################################################
 # BACKWARD OBJECT

external/backtrace-cpp/backward.hpp

@@ -1391,6 +1391,7 @@ private:
 					if (die_has_pc(die, pc)) {
 						return result;
 					}
+					/* fall through */
 				default:
 					bool declaration = false;
 					Dwarf_Attribute attr_mem;