GDB stub (#1583)

* gdbstub beginnings

* gdbstub: finish gdb impl things, next up is integration with melonDS

* holy fuck the gdbstub works

* gdb breakpoints work, but there's a mysterious crash on continue

* fix memory corruption that sometimes happened, and make resetting the console thru gdb work

* remove some gdb debug printing

* fix things in gdbstub

* separate option for enabling gdbstub

* add mode-dependent CPU registers

* C++ize the GDBstub code

* add gdbstub config in emu settings dialog

* make sure gdb is disabled when jit is enabled

* Remove unnecessary compiler flags, mark ARMJIT assembly code as no-execute-stack

This hardens the binary a little bit against common exploitation methods

* add option to wait for debugger attach on startup

* only insert GNU stack notes on linux

* disable gdbstub enable checkbox when jit is enabled

* fix non-linux incompatibilities

* enable gdbstub by default

* fix issues with gdbstub settings disable stuff

* format stuff

* update gdb test code

* Fix segfault when calling StubCallbacks->GetCPU()

C++ overrides are hard. Please I'm just a lowly C programmer.

* fix packet size not being sent correctly

Thanks to @GlowingUmbreon on Github for troubleshooting this

* fix select(2) calls (i should read docs more properly)

* fix GDB command sequencing/parsing issue (hopefully)

* [GDB] implement no-ack mode

* fix sending ack on handshake

* get lldb to work

src/frontend/qt_sdl/EmuSettingsDialog.ui

@@ -26,7 +26,7 @@
    <item>
     <widget class="QTabWidget" name="tabWidget">
      <property name="currentIndex">
-      <number>0</number>
+      <number>5</number>
      </property>
      <widget class="QWidget" name="tab">
       <attribute name="title">
@@ -568,6 +568,101 @@
        </item>
       </layout>
      </widget>
+     <widget class="QWidget" name="tab_6">
+      <attribute name="title">
+       <string>Devtools</string>
+      </attribute>
+      <layout class="QGridLayout" name="gridLayout_3">
+       <item row="1" column="0">
+        <widget class="QLabel" name="label_16">
+         <property name="text">
+          <string>ARM9 port</string>
+         </property>
+        </widget>
+       </item>
+       <item row="5" column="0">
+        <spacer name="verticalSpacer_4">
+         <property name="orientation">
+          <enum>Qt::Vertical</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>20</width>
+           <height>40</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+       <item row="2" column="0">
+        <widget class="QLabel" name="label_17">
+         <property name="text">
+          <string>ARM7 port</string>
+         </property>
+        </widget>
+       </item>
+       <item row="0" column="0" colspan="3">
+        <widget class="QCheckBox" name="cbGdbEnabled">
+         <property name="text">
+          <string>Enable GDB stub</string>
+         </property>
+        </widget>
+       </item>
+       <item row="4" column="0" colspan="7">
+        <widget class="QLabel" name="label_18">
+         <property name="text">
+          <string>Note: melonDS must be restarted in order for these changes to have effect</string>
+         </property>
+        </widget>
+       </item>
+       <item row="3" column="0" colspan="7">
+        <widget class="QLabel" name="label_19">
+         <property name="text">
+          <string>Note: GDB stub cannot be used together with the JIT recompiler</string>
+         </property>
+        </widget>
+       </item>
+       <item row="1" column="6">
+        <widget class="QCheckBox" name="cbGdbBOSA9">
+         <property name="text">
+          <string>Break on startup</string>
+         </property>
+        </widget>
+       </item>
+       <item row="1" column="1" colspan="5">
+        <widget class="QSpinBox" name="intGdbPortA9">
+         <property name="minimum">
+          <number>1000</number>
+         </property>
+         <property name="maximum">
+          <number>65535</number>
+         </property>
+         <property name="value">
+          <number>3333</number>
+         </property>
+        </widget>
+       </item>
+       <item row="2" column="1" colspan="5">
+        <widget class="QSpinBox" name="intGdbPortA7">
+         <property name="minimum">
+          <number>1000</number>
+         </property>
+         <property name="maximum">
+          <number>65535</number>
+         </property>
+         <property name="value">
+          <number>3334</number>
+         </property>
+        </widget>
+       </item>
+       <item row="2" column="6">
+        <widget class="QCheckBox" name="cbGdbBOSA7">
+         <property name="text">
+          <string>Break on startup</string>
+         </property>
+        </widget>
+       </item>
+      </layout>
+     </widget>
     </widget>
    </item>
    <item>
@@ -590,7 +685,6 @@
   </customwidget>
  </customwidgets>
  <tabstops>
-  <tabstop>tabWidget</tabstop>
   <tabstop>cbxConsoleType</tabstop>
   <tabstop>chkDirectBoot</tabstop>
   <tabstop>chkExternalBIOS</tabstop>
@@ -639,8 +733,8 @@
    <slot>accept()</slot>
    <hints>
     <hint type="sourcelabel">
-     <x>257</x>
-     <y>349</y>
+     <x>266</x>
+     <y>379</y>
     </hint>
     <hint type="destinationlabel">
      <x>157</x>
@@ -655,8 +749,8 @@
    <slot>reject()</slot>
    <hints>
     <hint type="sourcelabel">
-     <x>325</x>
-     <y>349</y>
+     <x>334</x>
+     <y>379</y>
     </hint>
     <hint type="destinationlabel">
      <x>286</x>