Can't find reference to libm in whetsonte and nbench

[Ycyken]

First of all, thank you for your benchmarks selection!
I encountered a bug when building the nbench and whetstone benchmarks using make, which was that it failed to link libm. I was using gcc 13.2.0 and ubuntu 24.04.
This happened because the -lm flag (in the CFLAGS variable) is before the input files (in the INPUT variable).

I have left a pull request with a solution for this problem.