Add support for UBSan's invalid builtin check

This is needed to check calls to __builtin_clz for a zero argument.
All our existing checks were optimized out because the compiler could
statically determine the operand was nonzero.

Bug: 136576760
Change-Id: I4f47e04e58a38c62b0bd87f6051776e5a588cff8
1 file changed