Fix function attribute LLVM API usage
Fix function attribute LLVM API usage

AFAICT, we don't need the index attributes so just use
Function::addFnAttr() API directly.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@iki.fi>

curtiszimmerman/libcpu,libcpu/libcpu,libcpu/libcpu,libcpu/libcpu,curtiszimmerman/libcpu,curtiszimmerman/libcpu,monocasa/libcpu,curtiszimmerman/libcpu,monocasa/libcpu,monocasa/libcpu,libcpu/libcpu,monocasa/libcpu