relational: create re-usable macros for relational declarations

relational.h includes relational macros for defining functions which need to
return 1 for scalar true and -1 for vector true.

I believe that this is the only place that this behavior is required, so the
macro is placed at its lowest useful level (same directory as it is used in).

This also creates re-usable unary/binary declaration and floatn includes which
should simplify relational builtin declarations.

Mostly patterned off of include/math/[binary_decl|unary_decl|floatn].inc
but with required changes for relational functions.

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
llvm-svn: 213315