move elf section uniquing to MCContext.  Along the way
merge XCore's section into MCSectionELF

llvm-svn: 100812
diff --git a/llvm/lib/Target/X86/X86MCAsmInfo.h b/llvm/lib/Target/X86/X86MCAsmInfo.h
index 69716bf..5815225 100644
--- a/llvm/lib/Target/X86/X86MCAsmInfo.h
+++ b/llvm/lib/Target/X86/X86MCAsmInfo.h
@@ -27,7 +27,7 @@
 
   struct X86ELFMCAsmInfo : public MCAsmInfo {
     explicit X86ELFMCAsmInfo(const Triple &Triple);
-    virtual MCSection *getNonexecutableStackSection(MCContext &Ctx) const;
+    virtual const MCSection *getNonexecutableStackSection(MCContext &Ctx) const;
   };
 
   struct X86MCAsmInfoCOFF : public MCAsmInfoCOFF {