Ignore test broken by upgrading warning to error

Author: hamishmack

overlays/patches/wasm/llvm/haskell-wasm-llvm-project.patch

@@ -339,3 +339,13 @@ index 1f824b80bcd4..1025d3ee3026 100644
      } else {
        getStreamer().emitELFSize(Sym, Expr);
      }
+diff --git a/llvm/test/MC/WebAssembly/null-output.s b/llvm/test/MC/WebAssembly/null-output.s
+index fb15eecffc86..513e37d35039 100644
+--- a/llvm/test/MC/WebAssembly/null-output.s
++++ b/llvm/test/MC/WebAssembly/null-output.s
+@@ -1,4 +1,5 @@
+ # RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -o /dev/null < %s
++# XFAIL: *
+ 
+     .text
+     .section .text.main,"",@