fix drem symbol for static linking and new targets

The compat remainder code is no longer built for !LIBM_SVID_COMPAT targets,
but the legacy drem, dremf and dreml symbols should be still defined since
removing them may break existing code, so keep them as aliases in the
non-compat remainder code.

	* math/w_remainder.c: New file.
	* math/w_remainderf.c: New file.
	* math/w_remainderl.c: New file.