Return a result from computeInputSections instead of mutating its argument.

This should improve readability.

llvm-svn: 299498
diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
index 6dc7051..d7405dd 100644
--- a/lld/ELF/LinkerScript.h
+++ b/lld/ELF/LinkerScript.h
@@ -225,10 +225,12 @@
 class LinkerScript {
 protected:
   void assignSymbol(SymbolAssignment *Cmd, bool InSec = false);
-  void computeInputSections(InputSectionDescription *);
   void setDot(Expr E, const Twine &Loc, bool InSec = false);
 
   std::vector<InputSectionBase *>
+  computeInputSections(const InputSectionDescription *);
+
+  std::vector<InputSectionBase *>
   createInputSectionList(OutputSectionCommand &Cmd);
 
   std::vector<size_t> getPhdrIndices(StringRef SectionName);