Core/HW: Add cpp-ipc submodule.

The last official release is, at the time of writing, almost two years
old. The latest development snapshot (updated ~2 months ago) will be
used.

.gitmodules

@@ -114,6 +114,10 @@
 	path = Externals/pugixml/pugixml
 	url = https://github.com/zeux/pugixml.git
 	shallow = true
+[submodule "Externals/cpp-ipc/cpp-ipc"]
+	path = Externals/cpp-ipc/cpp-ipc
+	url = https://github.com/mutouyun/cpp-ipc.git
+	shallow = true
 [submodule "Externals/cpp-optparse/cpp-optparse"]
 	path = Externals/cpp-optparse/cpp-optparse
 	url = https://github.com/weisslj/cpp-optparse.git

Externals/cpp-ipc/cpp-ipc

@@ -0,0 +1 @@
+Subproject commit a0c7725a1441d18bc768d748a93e512a0fa7ab52

Externals/licenses.md

@@ -8,6 +8,8 @@ Dolphin includes or links code of the following third-party software projects:
    [LGPLv2.1+](http://bochs.sourceforge.net/cgi-bin/lxr/source/COPYING)
 - [bzip2](https://www.sourceware.org/bzip2/):
    [bzip2 license](https://www.sourceware.org/git/?p=bzip2.git;a=blob;f=LICENSE;hb=HEAD) (similar to 3-clause BSD)
+- [cpp-ipc](https://github.com/mutouyun/cpp-ipc):
+   [MIT](https://github.com/mutouyun/cpp-ipc/blob/master/LICENSE)
 - [cubeb](https://github.com/kinetiknz/cubeb):
    [ISC](https://github.com/kinetiknz/cubeb/blob/master/LICENSE)
 - [Discord-RPC](https://github.com/discordapp/discord-rpc):