[REQUEST] Expose compilation option to disable/enable fmad instructions

[nvlukasz]

Description

Allow controlling whether compilers emit fused floating point instructions like fmad, since these instructions can affect numerical accuracy.

Context

We observed surprising floating point precision issues in Autodesk XLB and traced it down to fmad instructions. These can be disabled with the --fmad=false option to NVRTC.

[nvlukasz]

The simplest way to add this would be to include a boolean enable_fmad option in module or kernel options. This would be similar to the existing fast_math option.

However, we could consider doing something more general, like allowing users to specify arbitrary compiler options for each backend. This would likely be more work, but might result in a simpler and more flexible system.