[WebAssembly] Disable a test that violates DR1696

Summary:
lifetime2.C violates DR1696, which prevents reference members from being
initialized to temporaries, whose lifetime would end at the end of ctor.

Reviewers: sbc100

Subscribers: dschuff, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D49577

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337512 91177308-0d34-0410-b5e6-96231b3b80d8

Author: aheejin

lib/Target/WebAssembly/known_gcc_test_failures.txt

@@ -92,6 +92,7 @@ devirt-13.C  # bad main signature
 devirt-14.C  # bad main signature
 devirt-21.C  # bad main signature
 devirt-23.C  # bad main signature
+lifetime2.C  # violates C++ DR1696
 
 # Untriaged C++ failures
 spec5.C