[ThinLTO] Work around existing failure exposed by new test

When adding summary entries for index-based WPD (r364960), an added
test also included some additional testing of the existing hybrid
Thin/Regular LTO WPD (test/ThinLTO/X86/devirt.ll). That part of the
test is producing a failure on the llvm-clang-x86_64-expensive-checks-win
bot:

*** Bad machine code: Explicit definition marked as use ***
- function:    __typeid__ZTS1A_0_branch_funnel
- basic block: %bb.0  (0x81d4c58)
- instruction: ICALL_BRANCH_FUNNEL %0:gr64, @0, 16, @_ZN1B1fEi, 48, @_ZN1C1fEi
- operand 0:   %0:gr64
LLVM ERROR: Found 1 machine code errors.

This is functionality unrelated to the summary entries added with my
patch, so I am disabling this part of the new test until it is
addressed. I'll continue to investigate the failure.

llvm-svn: 364978