RFR(XS): 8171092: C1's Math.fma() intrinsic doesn't correctly process its inputs

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8171092/webrev.00/

3rd input of the fma intrinsic is processed as a temp but is actually an
input. The test case triggers the problem on aarch64 (with the patch
from 8162338). I couldn't get a failure on x86 because the input is
overwritten by the fma instruction: a copy of the input is made to a new
register right before the fma instruction and the input is live until
right before the fma instruction. I'm far from certain the bug cannot
show up on x86 with some other code pattern.

Roland.