[Patch AArch64] Fixup floating point division with -march=armv8-a+nosimd

[Patch AArch64] Fixup floating point division with -march=armv8-a+nosimd

The canonical examples is :

    double
    foo (double x, double y)
      {
        return x / y;
      }

    with -march=armv8-a+nosimd

generates a function that calls __divdf3. Ofcourse on AArch64 we don't
have any software floating point and this causes issues.

There is also a problem in +nosimd that has existed since the dawn of
time in the port with respect to long doubles (128 bit floating
point), here the ABI and the compiler expect the presence of the SIMD
unit as these parameters are passed in the vector registers. Thus
while +nosimd tries to prevent the use of SIMD instructions in the
compile we don't get this right as we end up using ldr qN / str qN
instructions and even there I think things go wrong in a simple
example that I tried.

Is that sufficient to consider marking +nosimd as deprecated in GCC-8
and remove this in a future release ?

That is not a subject for this patch but something separate but I
would like to put this into trunk and the release
branches. Bootstrapped and regression tested on my aarch64 desktop.

Ok ?

From-SVN: r255194