Fix anchor for small symmetrical column filters.

In the unoptimized version of small symmetrical column filters, when we
try to detect if the kernel, ky, is equal to [1;2;1] or [1;-2;1] we
should take into consideration that the anchor points in the middle
element.
Remove redundant -mfpu=neon flag.

This flag is already added in line 131.
Merge pull request #3436 from oresths:compiler_option
Merge pull request #3435 from oresths:filter_anchor_fix