* math/math.h (_Mfloat_, _Mlong_double_): New macros, defined iff not
already defined to float, long double. Use those macros for _Mdouble_
defns when including mathcalls.h.
* math/Makefile [$(long-double-fcts) != yes] (CPPFLAGS): Append
-D_Mlong_double_=double.
Add more -lm functions to -lc because ldexp uses them.
* math/Makefile (calls): Add s_finite, s_copysign, s_scalbn, s_modf.
(routines): Remove s_modf, add s_frexpf, s_ldexpf; all but frexp and
ldexp have both f and l code, and those have f though not l code.
memcpy for possibly overlapping strings.