[TESTSUITE] assert (char == signed char)

[Michael Snyder]

There seem to be some tests in the testsuite that are
based on the assumption that chars are signed, and that
will fail if they are unsigned.

Eg: 
sizeof.exp: check valueof ((int) (char)) -1 == -1
(prints 255 if char == unsigned)

pointers.exp: ptype pC
(outputs "unsigned char *" if char == unsigned)

Any thoughts?  Should these be regularized to accept unsigned?
Should it be based on a configure variable?