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
Include the mean again in the summary
Print out timing type as a benchmark level value

Print out the timing type as a benchmark level value instead of the
current function level value.
New script to import and process benchmark output

This is a utility script to import and process benchmark outputs.  It
loads a benchmark output file and validates it against a schema.  It
can then compress timing data and present the benchmark object with
reduced timings that should be representative of the detailed timings
data.

Programs can use this as a building block to construct their use cases
for analysis of the benchmarks.
benchtest: script to compare two benchmarks

This script is a sample implementation that uses import_bench to
construct two benchmark objects and compare them.  If detailed timing
information is available (when one does `make DETAILED=1 bench`), it
writes out graphs for all functions it benchmarks and prints
significant differences in timings of the two benchmark runs.  If
detailed timing information is not available, it points out
significant differences in aggregate times.

Call this script as follows:

  compare_bench.py schema_file.json bench1.out bench2.out

Alternatively, if one wants to set a different threshold for warnings
(default is a 10% difference):

  compare_bench.py schema_file.json bench1.out bench2.out 25

The threshold in the example above is 25%.  schema_file.json is the
JSON schema (which is $srcdir/benchtests/scripts/benchout.schema.json
for the benchmark output file) and bench1.out and bench2.out are the
two benchmark output files to compare.