[compiler-rt] [RISCV][compiler-rt] Asm funcs should be hidden (PR #226633)

[Sam Elliott via llvm-commits]

lenary wrote:

> > Should we be using the DEFINE_COMPILERRT_FUNCTION and/or DEFINE_COMPILERRT_PRIVATE_FUNCTION macros from compiler-rt/lib/builtins/assembly.h?
> 
> And while you are touching these files could you also add `END_COMPILERRT_FUNCTION`? Having precise .size information for these functions is nice to have too.

This is done, though I am not sure "precise size information" is entirely correct given the tail sharing going on.

https://github.com/llvm/llvm-project/pull/226633