[musl] scalbn.c and friends

[musl] scalbn.c and friends

[Damian McGuckin]

Probably more an FYI only:

I took some of the logic from an unrelated task to make a change to the 
code which involved biasing the exponent a little earlier than it is done 
currently for the case of a highly negative 2nd argument.

Using Godbolt, and -O3, the lines of assembler dropped somewhat for the 
newer code

 	CPU/Compiler	OLD => NEW
 	ARM gcc 13	47 -> 36
 	Power64 gcc 13	50 -> 42
 	X86 gcc 13	42 -> 35

Performance with my test machine, GCC 11 on X86, remains the same. So no 
speed gain. Not that it is doing much computation.

I assume that it is not worth touching this routine.

But the drop in LOC was interesting.  Probably just means that optimizing 
compilers are getting better which is not news to anybody

  - Damian