Auto merge of #33508 - alexcrichton:always-lower-frem, r=nikomatsakis

trans: Always lower to `frem`

Long ago LLVM unfortunately didn't handle the 32-bit MSVC case of `frem` where
it can't be lowered to `fmodf` because that symbol doesn't exist. That was since
fixed in http://reviews.llvm.org/D12099 (landed as r246615) and was released in
what appears to be LLVM 3.8. Now that we're using that branch of LLVM let's
remove our own hacks and help LLVM optimize a little better by giving it
knowledge about what we're doing.

diff --cc src/librustc_trans/expr.rs
Simple merge

diff --cc src/librustc_trans/mir/rvalue.rs
Simple merge