Add a std::make_unique implementation

Some compilers we care about (mostly g++) do not support std::make_unique yet,
but we still want to use it in our codebase to make unique_ptr code more
readable. This commit introduces an implementation derivated from the libc++
code in the Dolphin codebase so we can use it right now everywhere.

Adapted from delroth's pull request.

Source/Core/Common/Common.vcxproj

@@ -72,6 +72,7 @@
     <ClInclude Include="LinearDiskCache.h" />
     <ClInclude Include="Log.h" />
     <ClInclude Include="LogManager.h" />
+    <ClInclude Include="MakeUnique.h" />
     <ClInclude Include="MathUtil.h" />
     <ClInclude Include="MemArena.h" />
     <ClInclude Include="MemoryUtil.h" />