Dear all,

we did not recover well from bad expressions in array constructors,
especially when there was a typespec and a unary '+' or '-', and
when the array constructor was used in an arithmetic expression.

The attached patch introduces an ARITH_INVALID_TYPE that is used
when we try to recover from these errors, and tries to handle
all unary and binary arithmetic expressions.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

Thanks,
Harald