alpha: Fix missing inexact-flag raising in a lot of cases

alpha: Fix missing inexact-flag raising in a lot of cases

The alpha  uses -mieee, which is fully IEEE-compliant code except
that the inexact-flag.  However, a lot of functions now assumes
fully IEEE compliant, including inexact-flag.

This patch changes it to use -mieee-with-inexact instead, which
is simpler and more comprensible to just turn is implementation
by implementation (as done for fma).

The l*[rint|round]f codes uses alpha inline assembly, which also
not fully IEEE compliant.  Use the software fallback implementation
instead.