Implement the UNSIGNED extension type and operations under control of a
language feature flag (-funsigned).
This is nearly identical to the UNSIGNED feature that has been available
in Sun Fortran for years, and now implemented in GNU Fortran for
gfortran 15, and proposed for ISO standardization in J3/24-116.txt.
See the new documentation for details; but in short, this is C's
unsigned type, with guaranteed modular arithmetic for +, -, and *, and
the related transformational intrinsic functions SUM & al.
For testing purposes the implementations of the output APIs like
OutputInteger32 have been simply constructing descriptors and executing
the operation through the general DescriptorIO template. This patch
decouples those APIs from that mechanism so that programs using simple
"PRINT *" statements for output can link to a smaller portion of the I/O
runtime support library. (This is the only form of I/O accepted in GPU
device code by previous CUDA Fortran and Fortran OpenACC compilers.)
