MC/Mach-O: Factor out isSymbolLinkerVisible method; "linker visible" is a made up term to refer to non-temporary labels + temporary labels in sections-which-require symbols. For Darwin, it corresponds to symbols which effectively define an atom.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98923 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAssembler.h

@@ -636,6 +636,12 @@ private:
 
   // FIXME: Make protected once we factor out object writer classes.
 public:
+  /// Check whether a particular symbol is visible to the linker and is required
+  /// in the symbol table, or whether it can be discarded by the assembler. This
+  /// also effects whether the assembler treats the label as potentially
+  /// defining a separate atom.
+  bool isSymbolLinkerVisible(const MCSymbolData *SD) const;
+
   /// Evaluate a fixup to a relocatable expression and the value which should be
   /// placed into the fixup.
   ///