ELF: Change the return type of getSectionOrder.

Also changed the function name and added comments.

llvm-svn: 267044
diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
index d5195bc..d076f35 100644
--- a/lld/ELF/LinkerScript.h
+++ b/lld/ELF/LinkerScript.h
@@ -85,7 +85,7 @@
   int compareSections(StringRef A, StringRef B);
 
 private:
-  uint32_t getSectionOrder(StringRef Name);
+  int getSectionIndex(StringRef Name);
   SectionRule *find(InputSectionBase<ELFT> *S);
 
   ScriptConfiguration &Opt = *ScriptConfig;