Add support for reading ARM ELF build attributes.

Build attribute sections can now be read if they exist via ELFObjectFile, and
the llvm-readobj tool has been extended with an option to dump this information
if requested. Regression tests are also included which exercise these features.

Also update the docs with a fixed ARM ABI link and a new link to the Addenda
which provides the build attributes specification.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181009 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-readobj/ObjDumper.h

@@ -39,6 +39,7 @@ public:
   virtual void printDynamicTable() { }
   virtual void printNeededLibraries() { }
   virtual void printProgramHeaders() { }
+  virtual void printARMBuildAttributes() { }
 
 protected:
   StreamWriter& W;