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

llvm-svn: 206906
diff --git a/llvm/lib/MC/MCELFStreamer.cpp b/llvm/lib/MC/MCELFStreamer.cpp
index 4242b62..d42636e 100644
--- a/llvm/lib/MC/MCELFStreamer.cpp
+++ b/llvm/lib/MC/MCELFStreamer.cpp
@@ -275,11 +275,12 @@
   EmitCommonSymbol(Symbol, Size, ByteAlignment);
 }
 
-void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size) {
+void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
+                                  const SMLoc &Loc) {
   if (getCurrentSectionData()->isBundleLocked())
     report_fatal_error("Emitting values inside a locked bundle is forbidden");
   fixSymbolsInTLSFixups(Value);
-  MCObjectStreamer::EmitValueImpl(Value, Size);
+  MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
 }
 
 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,