don't set HasReliableSymbolDifference for ELF.

It is only used in MachObjectWriter.cpp. Another leftover from early days
of ELF in MC.

llvm-svn: 200895
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 1260208..a80be99 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -347,9 +347,7 @@
 public:
   uint8_t OSABI;
   ELFX86AsmBackend(const Target &T, uint8_t _OSABI, StringRef CPU)
-    : X86AsmBackend(T, CPU), OSABI(_OSABI) {
-    HasReliableSymbolDifference = true;
-  }
+      : X86AsmBackend(T, CPU), OSABI(_OSABI) {}
 };
 
 class ELFX86_32AsmBackend : public ELFX86AsmBackend {