alpha: Remove s_trunc{f} implementation (BZ#22666)

alpha: Remove s_trunc{f} implementation (BZ#22666)

As discussed in libc-alpha [1], alpha trunc{f} implementation uses
addt/suc and subt/suc and although the Alpha Architecture
Handbook version 3 states that that ADDx SUBx OUTPUT Exceptions
(B.3 Mapping to IEEE Standard) should not generate Inexact if INE
bit is set, the Alpha 21264 [2] chip manual (A.8 IEEE Floating-Point
Conformance) states that ADDx SUBx OUTPUT does generate inexact
exception for inexact result regardless.

As Joseph noted [3] to correctly fix it on alpha we need to either
avoid the instruction or avoid any inexact bit from it being set
on return from the function (while preserving the inexact bit that
might be set on the entry to the function).  The later will result
mf_fpcr followed by a mt_fpcr to get and set the fpcr which will
defeat the optimization itself.

So the patch just remove the alpha optimized and rely on generic
implementation.  It fixes the math/test-*-{trunc} on alpha.

        [BZ #15479]
        [BZ #22666]
        * sysdeps/alpha/fpu/s_trunc.c: Remove file.
        * sysdeps/alpha/fpu/s_truncf.c: Likewise.

[1] https://sourceware.org/ml/libc-alpha/2018-01/msg00114.html
[2] https://www.star.bnl.gov/public/daq/HARDWARE/21264_data_sheet.pdf
[3] https://sourceware.org/ml/libc-alpha/2018-01/msg00086.html

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>