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.

src/rustllvm/RustWrapper.cpp

@@ -907,10 +907,8 @@ LLVMRustDIBuilderCreateNameSpace(LLVMRustDIBuilderRef Builder,
       ,
       unwrapDI<DIFile>(File), LineNo
 #endif
-#if LLVM_VERSION_GE(4, 0)
       ,
       false // ExportSymbols (only relevant for C++ anonymous namespaces)
-#endif
       ));
 }
 
@@ -1547,14 +1545,6 @@ LLVMRustBuildVectorReduceFMax(LLVMBuilderRef, LLVMValueRef, bool) {
 }
 #endif
 
-#if LLVM_VERSION_LT(4, 0)
-extern "C" LLVMValueRef
-LLVMBuildExactUDiv(LLVMBuilderRef B, LLVMValueRef LHS,
-                   LLVMValueRef RHS, const char *Name) {
-  return wrap(unwrap(B)->CreateExactUDiv(unwrap(LHS), unwrap(RHS), Name));
-}
-#endif
-
 #if LLVM_VERSION_GE(6, 0)
 extern "C" LLVMValueRef
 LLVMRustBuildMinNum(LLVMBuilderRef B, LLVMValueRef LHS, LLVMValueRef RHS) {