test-link: correct expected object file name

The name of the ZCU object file emitted by the LLVM backend has been
changed in this branch from e.g. `foo.o` to `foo_zcu.o`. This is to
avoid name clashes. This commit just updates a link test which started
failing because the object name in a linker error changed.

Author: mlugg

test/link/macho.zig

@@ -211,7 +211,7 @@ fn testDuplicateDefinitions(b: *Build, opts: Options) *Step {
     expectLinkErrors(exe, test_step, .{ .exact = &.{
         "error: duplicate symbol definition: _strong",
         "note: defined by /?/a.o",
-        "note: defined by /?/main.o",
+        "note: defined by /?/main_zcu.o",
     } });
 
     return test_step;
@@ -2648,7 +2648,7 @@ fn testUnresolvedError(b: *Build, opts: Options) *Step {
         expectLinkErrors(exe, test_step, .{ .exact = &.{
             "error: undefined symbol: _foo",
             "note: referenced by /?/a.o:_bar",
-            "note: referenced by /?/main.o:_main.main",
+            "note: referenced by /?/main_zcu.o:_main.main",
         } });
     } else {
         expectLinkErrors(exe, test_step, .{ .exact = &.{