Register LLVM handlers for bad-alloc / OOM

LLVM's default bad-alloc handler may throw if exceptions are enabled,
and `operator new` isn't hooked at all by default. Now we register our
own handler that prints a message similar to fatal errors, then aborts.
We also call the function that registers the C++ `std::new_handler`.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1519,7 +1519,7 @@ extern "C" {
 
 #[link(name = "llvm-wrapper", kind = "static")]
 extern "C" {
-    pub fn LLVMRustInstallFatalErrorHandler();
+    pub fn LLVMRustInstallErrorHandlers();
     pub fn LLVMRustDisableSystemDialogsOnCrash();
 
     // Create and destroy contexts.