Support for type-generic libm function implementations libm

Support for type-generic libm function implementations libm

This defines a new classes of libm objects.  The
<func>_template.c file which is used in conjunction
with the new makefile hooks to derive variants for
each type supported by the target machine.

The headers math-type-macros-TYPE.h are used to supply
macros to a common implementation of a function in
a file named FUNC_template.c and glued togethor via
a generated file matching existing naming in the
build directory.

This has the properties of preserving the existing
override mechanism and not requiring any arcane
build system twiddling.  Likewise, it enables machines
to override these files without any additional work.

I have verified the built objects for ppc64, x86_64,
alpha, arm, and m68k do not change in any meaningful
way with these changes using the Fedora cross toolchains.
I have verified the x86_64 and ppc64 changes still run.