Handle floating point and aggregate return types in SysV-mips64 ABI

    
    SUMMARY:
    This patch adds support of floating point and aggregate return types in GetReturnValueObjectImpl() for mips64.
    
    Reviewers: clayborg, jingham
    Subscribers: mohit.bhakkad,  nitesh.jain, sagar, jaydeep, lldb-commits
    Differential Revision: http://reviews.llvm.org/D11641

llvm-svn: 245026