Refactor part of math Makefile

In order to support more types, the Makefile needs a few bits
shuffled.

F is explictly used as a placeholder to substitute for the
appropriate type suffix.  This removes the need to demangle
_r suffixed objects.

The variable libm-compat-calls is added to house any objects which
are only built to provide compat symbols within libm.  That is,
no newly added type should ever attempt building these.  Note,
k_standard* files have been added there.  By consensus they are
deprecated; in practice, we haven't gotten there yet.

New types would be added as noted in the comments preceding
type-TYPE-{suffix,routines,yes} variables.  However, some manual
additions will still need to be done to add appropriate flags
when building the various variants of libm-test.c for a new type.

Likewise, test-ildoubl is renamed test-ildouble for consistency's
sake.