Drop -mrecip completely.

`-mrecip` optimizes `x/y` to `x * 1/y` which can be convenient on some CPUs at the cost of slightly different results. This was introduced a few weeks ago by @VinInn due to alleged performance improvements that turned out to be not as large when running larger scale tests. Given it is not supported on clang we (@VinInn and myself) agreed to drop it for the moment. Notice also that probably `-freciprocal-math` provides the same level of optimization and it is also available on clang.