* add support for compiling Objective-C++ code
Prior to this change, calling `step.addCSourceFiles` with Obj-C++ file extensions
(`.mm`) would result in an error due to Zig not being aware of that extension.
Clang supports an `-ObjC++` compilation mode flag, but it was only possible to use
if you violated standards and renamed your `.mm` Obj-C++ files to `.m` (Obj-C) to
workaround Zig being unaware of the extension.
This change makes Zig aware of `.mm` files so they can be compiled, enabling compilation
of projects such as [Google's Dawn WebGPU](https://dawn.googlesource.com/dawn/) using
a `build.zig` file only.
Helps hexops/mach#21
Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
* test/standalone: add ObjC++ compilation/linking test
Based on the existing objc example, just tweaked for ObjC++.
Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
