[libc][arm] add more math.h entrypoints (#77839)

In particular, we have internal customers that would like to use nanf
and
scalbnf.

The differences between various entrypoint files can be checked via:

    $ comm -3 <(grep libc\.src path/to/entrypoints.txt | sort) \
       <(grep libc\.src path/to/other/entrypoints.txt | sort)