Include a source location when complaining about bad inline assembly.

Add a MI->emitError() method that the backend can use to report errors
related to inline assembly. Call it from X86FloatingPoint.cpp when the
constraints are wrong.

This enables proper clang diagnostics from the backend:

$ clang -c pr30848.c
pr30848.c:5:12: error: Inline asm output regs must be last on the x87 stack
  __asm__ ("" : "=u" (d));  /* { dg-error "output regs" } */
           ^
1 error generated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134307 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineInstr.h

@@ -22,6 +22,7 @@
 #include "llvm/ADT/ilist.h"
 #include "llvm/ADT/ilist_node.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/Support/DebugLoc.h"
 #include <vector>
@@ -180,6 +181,15 @@ public:
   ///
   DebugLoc getDebugLoc() const { return debugLoc; }
 
+  /// emitError - Emit an error referring to the source location of this
+  /// instruction. This should only be used for inline assembly that is somehow
+  /// impossible to compile. Other errors should have been handled much
+  /// earlier.
+  ///
+  /// If this method returns, the caller should try to recover from the error.
+  ///
+  void emitError(StringRef Msg) const;
+
   /// getDesc - Returns the target instruction descriptor of this
   /// MachineInstr.
   const MCInstrDesc &getDesc() const { return *MCID; }