Better diagnostics of vectorizing from GCC

Issue

• It would be nice if GCC gave a bit more user consumable diagnostics on when and why vectorizing fails.
• There is a really interesting thought regarding this in the hpcwire article The Heterogeneous Programming Jungle :

"Vectorizing compilers were successful for three very important reasons. The compilers not only attempted to vectorize your loops, they gave some very specific user feedback when they failed. How often does your optimizing compiler tell you when it failed to optimize your code? Never, most likely."