[BZ #6803] Set errno for scalbln, scalbn

Errno is not set and the testcases will fail.

Now the scalbln-aliases are removed in i386/m68
and the wrappers are used when calling the scalbln-functions.

On ia64 only scalblnf has its own implementation.
For scalbln and scalblnl the ieee754/dbl-64 and ieee754/ldbl-96 are used, thus
the wrappers are needed, too.