[gfortran] Front-end and library calls for large kinds

[FX Coudert]

[This mail is long, but you can read the first paragraph and then skip 
to the last one if you don't want the details]

Attached patch adds front-end and library support for mathematical 
functions taking real(10), real(16) and integer(16) argument(s). Right 
now, we do have minimal support for these kinds (can declare such 
variables, add/substract/multiply and divide them) and I/O support. What 
is missing is to be able to build function calls with them, such as:

   real(10) :: x = 2
   x = sqrt(x)

This requires modifications of the front-end, and library support (for 
functions other than those in libm). Attached patch provides front-end 
support for all such constructions, but library support is limited to 
some functions (set_exponent, fraction, ...). But, when this first patch 
will be reviewed, accepted and commited, adding other functions will be 
fairly easy.

An example on what we can now do on i686-linux can be found in attached 
file real10.f90.

Some details on the patch:

* For the library part, functions for all kinds are now protected by 
preprocessor directives such as "#if defined (HAVE_GFC_REAL_16)" to 
ensure that only code for available kinds is compiled

* For the front-end part, a choice had to be made. Attached patch adds 
support for all possible kinds, constructs all possible trees, while 
only those related to available kinds will ever be used on a given 
system. I modified the gfc_get_int_type and other gfc_get_*_type 
functions so that they don't issue an internal error if the kind does 
not exist, but return NULL.



This patch was regtesting on i686-linux. Could someone review it? I'm 
not asking for commit approval yet; since I don't know the guts of the 
front-end very well, I'd like someone familiar with it to tell me if the 
   way I do it is right. Steven, Paul or Steven, you seem to be the ones 
for this job, can one of you do it?

FX


PS: I will be out of town, with no internet access, from July 6th until 
the end of August. I do hope we can get this in good form before that. 
Otherwise, anybody is welcome to use this small piece of work any way 
they like to contribute large kinds support for gfortran!
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