Add mach_override as a 3rdparty dep and hook it into the OS X overlay.

Prior versions of mach_override were small (a single file),
and we just had its source live in the OS X overlay directory.

Newer versions of mach_override use libudis86, so the file count
goes up a fair bit. So much so that it doesn't make sense to
have it live inside the OS X overlay anymore.

Because of that, this commit moves it into 3rdparty.

.gitmodules

@@ -19,3 +19,6 @@
 [submodule "3rdparty/minhook-src"]
 	path = 3rdparty/minhook-src
 	url = https://github.com/mumble-voip/minhook.git
+[submodule "3rdparty/mach-override-src"]
+	path = 3rdparty/mach-override-src
+	url = [email protected]:rentzsch/mach_override.git

3rdparty/mach-override-build/mach-override-build.pro

@@ -0,0 +1,36 @@
+include(../../compiler.pri)
+
+BUILDDIR=$$basename(PWD)
+SOURCEDIR=$$replace(BUILDDIR,-build,-src)
+
+!exists(../$$SOURCEDIR/README.markdown) {
+  message("The $$SOURCEDIR/ directory was not found. Please update your submodules (git submodule update --init).")
+  error("Aborting configuration")
+}
+
+CONFIG(debug, debug|release) {
+  CONFIG += console
+  DESTDIR	= ../../debug
+}
+
+CONFIG(release, debug|release) {
+  DESTDIR	= ../../release
+}
+
+TEMPLATE = lib
+CONFIG -= qt
+CONFIG += debug_and_release
+CONFIG += staticlib
+VPATH	= ../mach-override-src
+TARGET = mach-override
+INCLUDEPATH = ../mach-override-src/ ../mach-override-src/libudis86
+
+SOURCES *= \
+  mach_override.c \
+  libudis86/decode.c \
+  libudis86/input.c \
+  libudis86/itab.c \
+  libudis86/syn-att.c \
+  libudis86/syn-intel.c \
+  libudis86/syn.c \
+  libudis86/udis86.c