knumber_float fix MSVC 2022 compiler issues with log2 and exp2

Fix MSVC 2022 compiler issue "C:\_\58afbb54\kcalc\knumber\knumber_float.cpp(15):
 error C2169: 'log2': intrinsic function, cannot be defined
C:\_\58afbb54\kcalc\knumber\knumber_float.cpp(19): warning C4273:
 'exp2': inconsistent dll linkage
C:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\ucrt\corecrt_math.h(506):
 note: see previous definition of 'exp2'".