Fixup r348306: Require x86 for test

The test breaks on buildbots that don't enable the x86 backend. Other
tests in this directory explicitly require x86, so this should do the
trick.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@348466 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/COFF/s_udt.s b/test/COFF/s_udt.s
index e7d253f..8ad342e 100644
--- a/test/COFF/s_udt.s
+++ b/test/COFF/s_udt.s
@@ -1,3 +1,4 @@
+# REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-windows-msvc < %s > %t.obj
 # RUN: lld-link /DEBUG:FULL /nodefaultlib /entry:main %t.obj /PDB:%t.pdb /OUT:%t.exe
 # RUN: llvm-pdbutil dump -types -globals -symbols -modi=0 %t.pdb | FileCheck %s