Rollup merge of rust-lang#60097 - cuviper:llvm8-mergefunc-use-aliases, r=rkruppe

Use -mergefunc-use-aliases for any LLVM >= 8

This functionality is not specific to Rust's LLVM, but any starting in LLVM 8.0,
as noted in <rust-lang#56358 (comment)>.

cc @nikic
r? @rkruppe

Author: Centril

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1382,7 +1382,6 @@ extern "C" {
     pub fn LLVMRustDebugMetadataVersion() -> u32;
     pub fn LLVMRustVersionMajor() -> u32;
     pub fn LLVMRustVersionMinor() -> u32;
-    pub fn LLVMRustIsRustLLVM() -> bool;
 
     pub fn LLVMRustAddModuleFlag(M: &Module, name: *const c_char, value: u32);
 

src/librustc_codegen_llvm/llvm_util.rs

@@ -61,7 +61,7 @@ unsafe fn configure_llvm(sess: &Session) {
         if sess.opts.debugging_opts.disable_instrumentation_preinliner {
             add("-disable-preinline");
         }
-        if llvm::LLVMRustIsRustLLVM() {
+        if get_major_version() >= 8 {
             match sess.opts.debugging_opts.merge_functions
                   .unwrap_or(sess.target.target.options.merge_functions) {
                 MergeFunctions::Disabled |

src/rustllvm/RustWrapper.cpp

@@ -613,14 +613,6 @@ extern "C" uint32_t LLVMRustVersionMinor() { return LLVM_VERSION_MINOR; }
 
 extern "C" uint32_t LLVMRustVersionMajor() { return LLVM_VERSION_MAJOR; }
 
-extern "C" bool LLVMRustIsRustLLVM() {
-#ifdef LLVM_RUSTLLVM
-  return 1;
-#else
-  return 0;
-#endif
-}
-
 extern "C" void LLVMRustAddModuleFlag(LLVMModuleRef M, const char *Name,
                                       uint32_t Value) {
   unwrap(M)->addModuleFlag(Module::Warning, Name, Value);