vector: prevent fused multiply-add being used in floatingLineTo

The test code now produces bit-identical results across platforms.

Fixes golang/go#21460.

Change-Id: I58b72dacf3c7930e2804b4e37bd3ccd9ef3dc2f0
Reviewed-on: https://go-review.googlesource.com/61024
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
1 file changed