Ada type in binding for C99 bool

[Florian Weimer]

* Joel Sherrill:

>> Whatever the answer is, it should be used to define Interfaces.C.Bool.
>> (I don't know what GCC's options for representing _Bool are, sorry.)

> It appears to be unsigned char or at least sizeof(bool)=1
> on the architectures I tried this test program on.

That's only half of the story.  The other half are the possible values
of *(char *)&x for some variable of type _Bool, and what the value of
(int)x is in those cases.