[Common] Call abort() instead of exit() in die()

Calling abort() has multiple advantages. First, it better matches the
semantic of DIE(_MSG) as it signals an abnormal process termination,
whereas exit() is a normal process termination (even though
potentially with an error exit code). Secondly, abort() throws
SIGABRT, which in turn triggers a coredump, hence the program's state
can be inspected afterwards.

emper/Common.cpp

 // SPDX-License-Identifier: LGPL-3.0-or-later
-// Copyright © 2020 Florian Schmaus
+// Copyright © 2020-2021 Florian Schmaus
 #include "Common.hpp"
 
 #include <cstdio>
@@ -12,5 +12,6 @@ void die(const char* message, bool usePerror) {
 	} else {
 		std::cerr << message << std::endl;
 	}
-	exit(EXIT_FAILURE);
+
+	abort();
 }