naked function attribute support for Mips

[reed kotler]

This issue of naked function attribute support for Mips has come up in 
the context of LLVM and in regards to maintaining compatibility with gcc.

It's my understanding that the idea of the naked function attribute was 
rejected for gcc Mips.

I'm curious as to why.

For LLVM it basically works just by nature of how LLVM works in its 
target independent part.

It will not emit the function prologue or epilogue.

It still emits the .frame, .mask and .fmask because that is Mips 
specific code that does not currently know about the naked function 
attribute, but that is a separate issue.

There is also the issue of the return statement but this also a separate 
non Mips specific issue and I will post that separately.

Tia.

Reed