[lld][MachO] Add missing test requirements

Similarly to the existing tests (e.g. stab.s) function-starts.s
is not supported on Windows.

GitOrigin-RevId: 98f1564b88579af1657a1d4a997baa66959e2ef3
diff --git a/test/MachO/function-starts.s b/test/MachO/function-starts.s
index d5e9e75..42d7d8c 100644
--- a/test/MachO/function-starts.s
+++ b/test/MachO/function-starts.s
@@ -1,4 +1,5 @@
-# REQUIRES: x86
+# REQUIRES: x86, shell
+# UNSUPPORTED: system-windows
 
 # RUN: split-file %s %t