Fix logic for generating llvm.type.test()s

CodeGenFunction::EmitTypeMetadataCodeForVCall() could output an
llvm.assume(llvm.type.test())when CFI was enabled, optimizing out the
vcall check. This case was only reached when: 1) CFI-vcall was enabled,
2) -fwhole-program-tables was specified, and 3)
-fno-sanitize-trap=cfi-vcall was specified.

Patch by Vlad Tsyrklevich!

Differential Revision: https://reviews.llvm.org/D36013

llvm-svn: 309622