llvm-mc: Add dummy MCStreamer implementation, (eventually) for use in profiling.

- Currently unused.

 - A few other random comment fixes lumped in.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78960 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCStreamer.h

@@ -221,6 +221,10 @@ namespace llvm {
     virtual void Finish() = 0;
   };
 
+  /// createNullStreamer - Create a dummy machine code streamer, which does
+  /// nothing. This is useful for timing the assembler front end.
+  MCStreamer *createNullStreamer(MCContext &Ctx);
+
   /// createAsmStreamer - Create a machine code streamer which will print out
   /// assembly for the native target, suitable for compiling with a native
   /// assembler.

include/llvm/Target/TargetRegistry.h

@@ -217,7 +217,7 @@ namespace llvm {
     /// the current host.  If no close target can be found, this returns null
     /// and sets the Error string to a reason.
     ///
-    /// Mainted for compatibility through 2.6.
+    /// Maintained for compatibility through 2.6.
     static const Target *getClosestTargetForJIT(std::string &Error);
 
     /// @}