[SystemZ] Add llvm::Triple::systemz

First step towards reinstating the SystemZ backend.  Tests will be
included in the main backend patch.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181007 91177308-0d34-0410-b5e6-96231b3b80d8
[SystemZ] Add ELF relocation support

Another step towards reinstating the SystemZ backend.  Tests will be
included in the main backend patch.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181008 91177308-0d34-0410-b5e6-96231b3b80d8
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