fix compilation on Solaris 10 with GNU C 3.4.3

This patch fixes compilation on Solaris 10 platform which provides
GNU C 3.4.3 by default by removing unsupported -ftree-vectorize option.
This may penalize Solaris 11, where GNU C 4.6.2 is provided but current
cabal does not support OSes version detection and Solaris 10 is still
supported (by Oracle) and will be at least till 2021 so let's support it
too.