[PATCH] Simplify C99 isgreater macros

[Joseph Myers]

On Tue, 26 Sep 2017, Wilco Dijkstra wrote:

> Simplify the C99 isgreater macros.  Although some support was added
> in GCC 2.97, not all targets added support until GCC 3.1.  Therefore
> only use the builtins in math.h from GCC 3.1 onwards, and defer to
> generic macros otherwise.  Improve the generic isunordered macro
> to use compares rather than call fpclassify twice - this is not only faster
> but also correct for signaling NaNs.
> 
> OK for commit?

OK if compilation has been tested for at least one configuration using 
each changed header, with or without fixes for the pre-existing formatting 
bugs (missing space before '(' in calls to __GNUC_PREREQ, __builtin_* and 
__typeof__).

-- 
Joseph S. Myers
joseph@codesourcery.com