Add libcpp option to test options

Author: SammyJames

lib/std/Build.zig

@@ -867,6 +867,7 @@ pub const TestOptions = struct {
     filters: []const []const u8 = &.{},
     test_runner: ?LazyPath = null,
     link_libc: ?bool = null,
+    link_libcpp: ?bool = null,
     single_threaded: ?bool = null,
     pic: ?bool = null,
     strip: ?bool = null,
@@ -896,6 +897,7 @@ pub fn addTest(b: *Build, options: TestOptions) *Step.Compile {
             .target = options.target orelse b.graph.host,
             .optimize = options.optimize,
             .link_libc = options.link_libc,
+            .link_libcpp = options.link_libcpp,
             .single_threaded = options.single_threaded,
             .pic = options.pic,
             .strip = options.strip,