Fix for PR 15235 libgfortran doesn't build on Solaris

[Rainer Orth]

Andrew Pinski writes:

> > The situation is somewhat mixed now:
> >
> > * On Solaris 10, most execution tests fail due to link failures:
> >   __builtin_isnan is missing.  This is a bug in Sun's <iso/math_c99.h>
> >   which doesn't work with non-Sun C99 compilers.  Apart from reporting 
> > this
> >   to Sun, this is fixincludes material.
> 
> This one might be able to be fixed by defining TARGET_C99_FUNCTIONS for
> Solaris10 and above if it supports all C99 functions.

No, this won't help at all: even in that case, GCC won't provide a
__builtin_isnan.  See tm.texi for TARGET_C99_FUNCTIONS:

@defmac TARGET_C99_FUNCTIONS
When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
@code{sinf} and similarly for other functions defined by C99 standard.  The
default is nonzero that should be proper value for most modern systems, however
number of existing systems lacks support for these functions in the runtime so
they needs this macro to be redefined to 0.
@end defmac

But otherwise you're right: if Solaris 10 provides a complete ISO C99
library which is usable by GCC, then we should have e.g. sol10.h which
defines that macro.

	Rainer