TMP: probes for math functions

Temporary probes at various branch points in the functions.
Implement benchmarking script in python
Detailed benchmark numbers

Store timings per input.
Remove bench-modf.c
Add machine info
Make bench.out in json format
Actually do json output
benchtests: Mention a constraint on a valid variant name
benchtests: Move bench.py to benchtests/scripts/
benchtests: move machine-info.sh into benchtests/scripts/
Validate bench.out against a JSON schema