Support -C passes in NewPM

And report an error if parsing the additional pass pipeline fails.
Threading through the error accounts for most of the changes here.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2208,7 +2208,9 @@ extern "C" {
         llvm_selfprofiler: *mut c_void,
         begin_callback: SelfProfileBeforePassCallback,
         end_callback: SelfProfileAfterPassCallback,
-    );
+        ExtraPasses: *const c_char,
+        ExtraPassesLen: size_t,
+    ) -> LLVMRustResult;
     pub fn LLVMRustPrintModule(
         M: &'a Module,
         Output: *const c_char,