Fix the assembler to print a better relocatable expression error

diagnostic that includes location information.

Currently if one has this assembly:

	.quad (0x1234 + (4 * SOME_VALUE))

where SOME_VALUE is undefined ones gets the less than
useful error message with no location information:

% clang -c x.s
clang -cc1as: fatal error: error in backend: expected relocatable expression

With this fix one now gets a more useful error message
with location information:

% clang -c x.s 
x.s:5:8: error: expected relocatable expression
 .quad (0x1234 + (4 * SOME_VALUE))
       ^

To do this I plumbed the SMLoc through the MCObjectStreamer
EmitValue() and EmitValueImpl() interfaces so it could be used
when creating the MCFixup.

rdar://12391022


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206906 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCELFStreamer.h

@@ -72,7 +72,8 @@ public:
                     uint64_t Size = 0, unsigned ByteAlignment = 0) override;
   void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
                       uint64_t Size, unsigned ByteAlignment = 0) override;
-  void EmitValueImpl(const MCExpr *Value, unsigned Size) override;
+  void EmitValueImpl(const MCExpr *Value, unsigned Size,
+                     const SMLoc &Loc = SMLoc()) override;
 
   void EmitFileDirective(StringRef Filename) override;
 

include/llvm/MC/MCObjectStreamer.h

@@ -81,7 +81,8 @@ public:
   void EmitLabel(MCSymbol *Symbol) override;
   void EmitDebugLabel(MCSymbol *Symbol) override;
   void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) override;
-  void EmitValueImpl(const MCExpr *Value, unsigned Size) override;
+  void EmitValueImpl(const MCExpr *Value, unsigned Size,
+                     const SMLoc &Loc = SMLoc()) override;
   void EmitULEB128Value(const MCExpr *Value) override;
   void EmitSLEB128Value(const MCExpr *Value) override;
   void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) override;

include/llvm/MC/MCStreamer.h

@@ -529,9 +529,12 @@ public:
   /// @param Value - The value to emit.
   /// @param Size - The size of the integer (in bytes) to emit. This must
   /// match a native machine width.
-  virtual void EmitValueImpl(const MCExpr *Value, unsigned Size) = 0;
+  /// @param Loc - The location of the expression for error reporting.
+  virtual void EmitValueImpl(const MCExpr *Value, unsigned Size,
+                             const SMLoc &Loc = SMLoc()) = 0;
 
-  void EmitValue(const MCExpr *Value, unsigned Size);
+  void EmitValue(const MCExpr *Value, unsigned Size,
+                 const SMLoc &Loc = SMLoc());
 
   /// EmitIntValue - Special case of EmitValue that avoids the client having
   /// to pass in a MCExpr for constant integers.