libm -fno-builtin

[Jon Beniston]

Hi Wilco,

>Note -fno-math-errno is also a good option to add for libm since it enables
>more inlining. I added it to GLIBC a while back, no issues found since.

This causes a problem for sqrtl when _LDBL_EQ_DBL is defined. The call to
sqrt is replaced with a sqrt instruction, so errno will not be set.

I can't see many improvements in the code otherwise (there's a few changes
in scheduling) - but perhaps that is target specific.

Cheers,
Jon