Previously, TCC wrongly discarded the const and
volatile qualifiers from parameter types when
adjusting them.
- convert_parameter_type() will no longer remove
the const and volatile qualifiers from a CType.
- a new function, convert_expression_type(), will
remove the const and volatile qualifiers before
tail-calling convert_parameter_type().
- unary() and gexpr() will call
convert_expression_type() instead of
convert_parameter_type() to ensure that
expression semantics are unchanged.
The new tests for restrict also pass, but only
because the restrict keyword is ignored.
