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

[Alexander Richardson via llvm-commits]

arichardson 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.

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