Added long 'print-values' option for var-update MI command.

Summary:
The -var-update MI command should take the same print-values options as var-list children, however currently only the integer versions are supported.
Added --no-values, --all-values, and --simple-values long options. 

See:
https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Variable-Objects.html#GDB_002fMI-Variable-Objects

Patch from ewan@codeplay.com

Reviewers: EwanCrawford

Subscribers: ki.stfu, lldb-commits

Differential Revision: http://reviews.llvm.org/D8008

llvm-svn: 231233