[Bitstream] Temporarily disable UBSan for invalid bitcode tests. This fixes...

[Bitstream] Temporarily disable UBSan for invalid bitcode tests. This fixes failing sanitizer buildbots.

Tests added by
  https://github.com/llvm/llvm-project/commit/3c86642edd28f1ce970882edaba8dce468ec7401
  https://github.com/llvm/llvm-project/commit/f4fca0fbb052e55935b483c8955c440b59511ce8
cause existing code to exhibit UB:
  https://github.com/llvm/llvm-project/blob/b4c6d1bb379192cb5b712fda9f60cd105f21194f/llvm/include/llvm/Bitstream/BitstreamReader.h#L244

llvm/include/llvm/Bitstream/BitstreamReader.h:244:51:
runtime error: shift exponent 35 is too large for 32-bit type 'unsigned int'

Hitting the UBSan error before the expected error causes the test to fail under UBSan:

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D119182