change -ffast-math to less optimised options

[shadisharba]

This PR closes issue #126. -ffast-math is swapped with:

• -fassociative-math Allow re-association of operands in series of floating-point operations.
• -fno-signed-zeros Allow optimizations for floating-point arithmetic that ignore the signedness of zero.
• -fno-trapping-math Compile code assuming that floating-point operations cannot generate user-visible traps.
• -fno-math-errno Do not set errno after calling math functions that are executed with a single instruction, e.g., sqrt.

In this case all tests still pass even the ones checking for infs or nans