QTest::CrashHandler: ask GDB for the memory mapping layout on crash too

Processes usually crash due to invalid pointers, but sometimes it's hard
to know if a given value is valid or not just by eyeballing it. So let's
ask GDB to print it.

I don't think LLDB has a way to do it.

Change-Id: I35e35bd3b79eeba49192fffd61474054cd089301
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
(cherry picked from commit 2da64908c250203c7d17031a6b5c1d769b6215a2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/testlib/qtestcrashhandler.cpp

@@ -360,6 +360,7 @@ void generateStackTrace()
             break;
         case Gdb:
             execlp("gdb", "gdb", "--nx", "--batch", "-ex", "thread apply all bt",
+                   "-ex", "info proc mappings",
                    "--pid", pidbuffer.array.data(), nullptr);
             break;
         case Lldb: