neon: Enable Flush-to-zero mode for float programs

Some of the instructions are not NEON (which always uses FTZ),
but are actually VFP, which requires enabling FTZ mode.
5 jobs for neon in 2 minutes and 32 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #635727
debian sid

00:00:36

passed #635730
1607 windows docker
msys2

00:00:57

passed #635728
1607 windows docker
vs2017 amd64

00:01:07

passed #635779
1607 windows docker
vs2017 x86

00:01:01

failed #635729
1607 windows docker
vs2017 x86

00:00:00