[clang] [compiler-rt] Fix "[clang][UBSan] Add implicit conversion check for bitfields" (PR #87761)

[Axel Lundberg via cfe-commits]

Zonotora wrote:

@vitalybuka yes, seems like all testcases failed due to not explicitly setting BitfieldBits to 0  except one,
  LeakSanitizer-AddressSanitizer-i386 :: TestCases/leak_check_at_exit.cpp
not really sure what the problem is. Also added another testcase `ubsan/TestCases/ImplicitConversion/bitfield-conversion.c` to make sure it works properly.

https://github.com/llvm/llvm-project/pull/87761