Auto merge of #55593 - nikic:remove-llvm-4-checks, r=rkruppe

Remove checks for LLVM < 4.0

While we still have to support LLVM 4.0 for Emscripten, we can drop checks for LLVM >= 4.0 and < 4.0.

diff --cc src/librustc_codegen_llvm/back/write.rs
index a88ce69604b356fb90d5f85df4edf349e4739827,dabfa4c540b19589f5c4bfc5aef25b2e34182cf6..d04e80195f054afcb155a8823a099767c11e0e94
--- 1/src/librustc_codegen_llvm/back/write.rs
--- 2/src/librustc_codegen_llvm/back/write.rs
+++ b/src/librustc_codegen_llvm/back/write.rs
@@@ -10,8 -10,11 +10,8 @@@
  
  use attributes;
  use back::bytecode::{self, RLIB_BYTECODE_EXTENSION};
- use back::lto::{self, ModuleBuffer, ThinBuffer, SerializedModule};
+ use back::lto::{self, ThinBuffer, SerializedModule};
  use back::link::{self, get_linker, remove};
 -use back::command::Command;
 -use back::linker::LinkerInfo;
 -use back::symbol_export::ExportedSymbols;
  use base;
  use consts;
  use memmap;

diff --cc src/librustc_codegen_llvm/base.rs
Simple merge