sparc: Fix llrint and llround missing exceptions on SPARC V8

Conversions from a float to a long long on SPARC v8 uses a libgcc function
that may not raise the correct exceptions on overflow. It also may raise
spurious "inexact" exceptions on non overflow cases. This patch fixes the
problem in the same way as for RV32.

Signed-off-by: Daniel Cederman <cederman@gaisler.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>