ARM IAS: handle errors more appropriately

Directive parsers must return false if the target assembler is interested in
handling the directive.  The Error member function returns true always.  Using
the 'return Error()' pattern would incorrectly indicate to the general parser
that the target was not interested in the directive, when in reality it simply
encountered a badly formed directive or some other error.  This corrects the
behaviour to ensure that the parser behaves appropriately.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198132 91177308-0d34-0410-b5e6-96231b3b80d8
CodeGen: silence a C++11 feature warning

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198133 91177308-0d34-0410-b5e6-96231b3b80d8