fix: give a type to bad cond expr with known condition

fix: give a type to bad cond expr with known condition

Conditional expressions whose second & third operands
have non-compatible types are not conform to the C standard
and sparse emit a warning for them and return the expression
as being erroneous. In consequence, such expressions are not
given a type. This, in turn, makes that some further processing
cannot be done (correctly).

It seems that neither GCC nor clang emit a warning when
there is a type mismatch but the condition is a constant.

In the case we're interested here (the slow compilation of a file)
the operation that cannot be done is the expansion its operands.
This, in turn and among other things, makes that builtins like
__builtin_constant_p() are not evaluated with disatrous consequence
for the amount of work done in the next phases.

Fix this by giving to conditional expressions with constant
condition the same type as the operand selected by the conditional
(but keeping the warning) as GCC & clang seems to do.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>