PATCH: Add SSE4.1 support

[Richard Kenner]

> I am not able to generate 2 different templates with the same name,
> umaxv8hi3, depending on TARGET_SSE4_1 or TARGET_SSE2.

I'm missing something.  Why don't you have the define_expand for umaxvhi3
with the or of the conditions, then its text is to call whichever of the
two define_expands is appropriate and they have names like umaxv8hi3_41
and umaxv8hi3_2?